Bulk annealing of glass sheets

ABSTRACT

Surface modification layers and associated heat treatments, that may be provided on a sheet, a carrier, or both, to control both room-temperature van der Waals (and/or hydrogen) bonding and high temperature covalent bonding between the thin sheet and carrier. The room-temperature bonding is controlled so as to be sufficient to hold the thin sheet and carrier together during vacuum processing, wet processing, and/or ultrasonic cleaning processing, for example. And at the same time, the high temperature covalent bonding is controlled so as to prevent a permanent bond between the thin sheet and carrier during high temperature processing, as well as maintain a sufficient bond to prevent delamination during high temperature processing.

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. Provisional Application Ser. No. 61/791,418, filed on Mar. 15,2013, and of U.S. Provisional Application Ser. No. 61/736,862 filed onDec. 13, 2012, the content of which are relied upon and incorporatedherein by reference in their entireties.

BACKGROUND

1. Field of the Invention

The present invention is directed to articles and methods for processingflexible sheets on carriers and, more particularly to articles andmethods for processing flexible glass sheets on glass carriers.

2. Technical Background

Flexible substrates offer the promise of cheaper devices usingroll-to-roll processing, and the potential to make thinner, lighter,more flexible and durable displays. However, the technology, equipment,and processes required for roll-to-roll processing of high qualitydisplays are not yet fully developed. Since panel makers have alreadyheavily invested in toolsets to process large sheets of glass,laminating a flexible substrate to a carrier and making display devicesby a sheet-to-sheet processing offers a shorter term solution to developthe value proposition of thinner, lighter, and more flexible displays.Displays have been demonstrated on polymer sheets for examplepolyethylene naphthalate (PEN) where the device fabrication was sheet tosheet with the PEN laminated to a glass carrier. The upper temperaturelimit of the PEN limits the device quality and process that can be used.In addition, the high permeability of the polymer substrate leads toenvironmental degradation of OLED devices where a near hermetic packageis required. Thin film encapsulation offers the promise to overcome thislimitation, but it has not yet been demonstrated to offer acceptableyields at large volumes.

In a similar manner, display devices can be manufactured using a glasscarrier laminated to one or more thin glass substrates. It isanticipated that the low permeability and improved temperature andchemical resistance of the thin glass will enable higher performancelonger lifetime flexible displays.

However, the thermal, vacuum, solvent and acidic, and ultrasonic, FlatPanel Display (FPD) processes require a robust bond for thin glass boundto a carrier. FPD processes typically involve vacuum deposition(sputtering metals, transparent conductive oxides and oxidesemiconductors, Chemical Vapor Deposition (CVD) deposition of amorphoussilicon, silicon nitride, and silicon dioxide, and dry etching of metalsand insulators), thermal processes (including ˜300-400° C. CVDdeposition, up to 600° C. p-Si crystallization, 350-450° C. oxidesemiconductor annealing, up to 650° C. dopant annealing, and ˜200-350°C. contact annealing), acidic etching (metal etch, oxide semiconductoretch), solvent exposure (stripping photoresist, deposition of polymerencapsulation), and ultrasonic exposure (in solvent stripping ofphotoresist and aqueous cleaning, typically in alkaline solutions).

Adhesive wafer bonding has been widely used in Micromechanical Systems(MEMS) and semiconductor processing for back end steps where processesare less harsh. Commercial adhesives by Brewer Science and Henkel aretypically thick polymer adhesive layers, 5-200 microns thick. The largethickness of these layers creates the potential for large amounts ofvolatiles, trapped solvents, and adsorbed species to contaminate FPDprocesses. These materials thermally decompose and outgas above ˜250° C.The materials also may cause contamination in downstream steps by actingas a sink for gases, solvents and acids which can outgas in subsequentprocesses.

U.S. Provisional Application Ser. No. 61/596,727 filed on Feb. 8, 2012,entitled Processing Flexible Glass with a Carrier (hereinafter US '727)discloses that the concepts therein involve bonding a thin sheet, forexample, a flexible glass sheet, to a carrier initially by van der Waalsforces, then increasing the bond strength in certain regions whileretaining the ability to remove portions of the thin sheet afterprocessing the thin sheet/carrier to form devices (for example,electronic or display devices, components of electronic or displaydevices, organic light emitting device (OLED) materials, photo-voltaic(PV) structures, or thin film transistors), thereon. At least a portionof the thin glass is bonded to a carrier such that there is preventeddevice process fluids from entering between the thin sheet and carrier,whereby there is reduced the chance of contaminating downstreamprocesses, i.e., the bonded seal portion between the thin sheet andcarrier is hermetic, and in some preferred embodiments, this sealencompasses the outside of the article thereby preventing liquid or gasintrusion into or out of any region of the sealed article.

US '727 goes on to disclose that in low temperature polysilicon (LTPS)(low temperature compared to solid phase crystallization processingwhich can be up to about 750° C.) device fabrication processes,temperatures approaching 600° C. or greater, vacuum, and wet etchenvironments may be used. These conditions limit the materials that maybe used, and place high demands on the carrier/thin sheet. Accordingly,what is desired is a carrier approach that utilizes the existing capitalinfrastructure of the manufacturers, enables processing of thin glass,i.e., glass having a thickness≦0.3 mm thick, without contamination orloss of bond strength between the thin glass and carrier at higherprocessing temperatures, and wherein the thin glass de-bonds easily fromthe carrier at the end of the process.

One commercial advantage to the approach disclosed in US '727 is that,as noted in US '727, manufacturers will be able to utilize theirexisting capital investment in processing equipment while gaining theadvantages of the thin glass sheets for PV, OLED, LCDs and patternedThin Film Transistor (TFT) electronics, for example. Additionally, thatapproach enables process flexibility, including: that for cleaning andsurface preparation of the thin glass sheet and carrier to facilitatebonding; that for strengthening the bond between the thin sheet andcarrier at the bonded area; that for maintaining releasability of thethin sheet from the carrier at the non-bonded (or reduced/low-strengthbond) area and that for cutting the thin sheets to facilitate extractionfrom the carrier.

In the glass-to-glass bonding process, the glass surfaces are cleaned toremove all metal, organic and particulate residues, and to leave amostly silanol terminated surface. The glass surfaces are first broughtinto intimate contact where van der Waals and/or Hydrogen-bonding forcespull them together. With heat and optionally pressure, the surfacesilanol groups condense to form strong covalent Si—O—Si bonds across theinterface, permanently fusing the glass pieces. Metal, organic andparticulate residue will prevent bonding by obscuring the surfacepreventing the intimate contact required for bonding. A high silanolsurface concentration is also required to form a strong bond as thenumber of bonds per unit area will be determined by the probability oftwo silanol species on opposing surfaces reacting to condense out water.Zhuravlel has reported the average number of hydroxyls per nm² for wellhydrated silica as 4.6 to 4.9. Zhuravlel, L. T., The Surface Chemistryof Amorphous Silika, Zhuravlev Model, Colloids and Surfaces A:Physiochemical Engineering Aspects 173 (2000) 1-38. In US '727, anon-bonding region is formed within a bonded periphery, and the primarymanner described for forming such non-bonding area is increasing surfaceroughness. An average surface roughness of greater than 2 nm Ra canprevent glass to glass bonds forming during the elevated temperature ofthe bonding process. In U.S. Provisional Patent Application Ser. No.61/736,880, filed on Dec. 13, 2012 by the same inventors and entitledFacilitated Processing for Controlling Bonding Between Sheet and Carrier(hereinafter US '880), a controlled bonding area is formed bycontrolling the van der Waals and/or hydrogen bonding between a carrierand a thin glass sheet, but a covalent bonding area is still used aswell. Thus, although the articles and methods for processing thin sheetswith carriers in US '727 and US '880 are able to withstand the harshenvironments of FPD processing, undesirably for some applications, reuseof the carrier is prevented by the strong covalent bond between thinglass and glass carrier in the bonding region that is bonded bycovalent, for example Si—O—Si, bonding with adhesive force˜1000-2000mJ/m², on the order of the fracture strength of the glass. Prying orpeeling cannot be used to separate the covalently bonded portion of thethin glass from the carrier and, thus, the entire thin sheet cannot beremoved from the carrier. Instead, the non-bonded areas with the devicesthereon are scribed and extracted leaving a bonded periphery of the thinglass sheet on the carrier.

SUMMARY

In light of the above, there is a need for a thin sheet-carrier articlethat can withstand the rigors of the FPD processing, including hightemperature processing (without outgassing that would be incompatiblewith the semiconductor or display making processes in which it will beused), yet allow the entire area of the thin sheet to be removed (eitherall at once, or in sections) from the carrier so as to allow the reuseof the carrier for processing another thin sheet. The presentspecification describes ways to control the adhesion between the carrierand thin sheet to create a temporary bond sufficiently strong to surviveFPD processing (including LTPS processing) but weak enough to permitdebonding of the sheet from the carrier, even after high-temperatureprocessing. Such controlled bonding can be utilized to create an articlehaving a re-usable carrier, or alternately an article having patternedareas of controlled bonding and covalent bonding between a carrier and asheet. More specifically, the present disclosure provides surfacemodification layers (including various materials and associated surfaceheat treatments), that may be provided on the thin sheet, the carrier,or both, to control both room-temperature van der Waals, and/orhydrogen, bonding and high temperature covalent bonding between the thinsheet and carrier. Even more specifically, the room-temperature bondingmay be controlled so as to be sufficient to hold the thin sheet andcarrier together during vacuum processing, wet processing, and/orultrasonic cleaning processing. And at the same time, the hightemperature covalent bonding may be controlled so as to prevent apermanent bond between the thin sheet and carrier during hightemperature processing, as well as maintain a sufficient bond to preventdelamination during high temperature processing. In alternativeembodiments, the surface modification layers may be used to createvarious controlled bonding areas (wherein the carrier and sheet remainsufficiently bonded through various processes, including vacuumprocessing, wet processing, and/or ultrasonic cleaning processing),together with covalent bonding regions to provide for further processingoptions, for example, maintaining hermeticity between the carrier andsheet even after dicing the article into smaller pieces for additionaldevice processing. Still further, some surface modification layersprovide control of the bonding between the carrier and sheet while, atthe same time, reduce outgassing emissions during the harsh conditionsin an FPD (for example LTPS) processing environment, including hightemperature and/or vacuum processing, for example.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing thevarious aspects as exemplified in the written description and theappended drawings. It is to be understood that both the foregoinggeneral description and the following detailed description are merelyexemplary of the various aspects, and are intended to provide anoverview or framework to understanding the nature and character of theinvention as it is claimed.

The accompanying drawings are included to provide a furtherunderstanding of principles of the invention, and are incorporated inand constitute a part of this specification. The drawings illustrate oneor more embodiment(s), and together with the description serve toexplain, by way of example, principles and operation of the invention.It is to be understood that various features disclosed in thisspecification and in the drawings can be used in any and allcombinations. By way of non-limiting example the various features may becombined with one another as set forth at the end of the specificationas aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an article having carrier bonded to athin sheet with a surface modification layer therebetween.

FIG. 2 is an exploded and partially cut-away view of the article in FIG.1.

FIG. 3 is a graph of surface hydroxyl concentration on silica as afunction of temperature.

FIG. 4 is a graph of the surface energy of an SC1-cleaned sheet of glassas a function annealing temperature

FIG. 5 is a graph of the surface energy of a thin fluoropolymer filmdeposited on a sheet of glass as a function of the percentage of one ofthe constituent materials from which the film was made.

FIG. 6 is a schematic top view of a thin sheet bonded to a carrier bybonding areas.

FIG. 7 is a schematic side view of a stack of glass sheets

FIG. 8 is an exploded view of one embodiment of the stack in FIG. 7.

FIG. 9 is a schematic view of a testing setup

FIG. 10 is a collection of graphs of surface energy (of different partsof the test setup of FIG. 9) versus time for a variety of materialsunder different conditions.

FIG. 11 is a graph of change in % bubble area versus temperature for avariety of materials.

FIG. 12 is another graph of change in % bubble area versus temperaturefor a variety of materials.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation andnot limitation, example embodiments disclosing specific details are setforth to provide a thorough understanding of various principles of thepresent invention. However, it will be apparent to one having ordinaryskill in the art, having had the benefit of the present disclosure, thatthe present invention may be practiced in other embodiments that departfrom the specific details disclosed herein. Moreover, descriptions ofwell-known devices, methods and materials may be omitted so as not toobscure the description of various principles of the present invention.Finally, wherever applicable, like reference numerals refer to likeelements.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another embodiment includes from the one particular valueand/or to the other particular value. Similarly, when values areexpressed as approximations, by use of the antecedent “about,” it willbe understood that the particular value forms another embodiment. Itwill be further understood that the endpoints of each of the ranges aresignificant both in relation to the other endpoint, and independently ofthe other endpoint.

Directional terms as used herein—for example up, down, right, left,front, back, top, bottom—are made only with reference to the figures asdrawn and are not intended to imply absolute orientation.

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to a “component” includes aspects having two or moresuch components, unless the context clearly indicates otherwise.

In both U.S. 61/596,727, filed on Feb. 8, 2012, entitled ProcessingFlexible Glass with a Carrier and U.S. 61/736,880 (filed on Dec. 13,2012, entitled Facilitated Processing for Controlling Bonding BetweenSheet and Carrier), there are provided solutions for allowing theprocessing of a thin glass sheet on a carrier, whereby at least portionsof the thin glass sheet remain “non-bonded” so that devices processed onthe thin glass sheet may be removed from the carrier. However, theperiphery of the thin glass is permanently (or covalently, orhermetically) bonded to the carrier glass through the formation ofcovalent Si—O—Si bonds. This covalently bonded perimeter prevents reuseof the carrier, as the thin glass cannot be removed in this permanentlybonded zone without damaging the thin glass and carrier.

In order to maintain advantageous surface shape characteristics, thecarrier is typically a display grade glass substrate. Accordingly, insome situations, it is wasteful and expensive to merely dispose of thecarrier after one use. Thus, in order to reduce costs of displaymanufacture, it is desirable to be able to reuse the carrier to processmore than one thin sheet substrate. The present disclosure sets fortharticles and methods for enabling a thin sheet to be processed throughthe harsh environment of the FPD processing lines, including hightemperature processing—wherein high temperature processing is processingat a temperature≧400° C., and may vary depending upon the type of devicebeing made, for example, temperatures up to about 450° C. as inamorphous silicon or amorphous indium gallium zinc oxide (IGZO)backplane processing, up to about 500-550° C. as in crystalline IGZOprocessing, or up to about 600-650° C. as is typical in LTPSprocesses—and yet still allows the thin sheet to be easily removed fromthe carrier without damage (for example, wherein one of the carrier andthe thin sheet breaks or cracks into two or more pieces) to the thinsheet or carrier, whereby the carrier may be reused.

As shown in FIGS. 1 and 2, a glass article 2 has a thickness 8, andincludes a carrier 10 having a thickness 18, a thin sheet 20 (i.e., onehaving a thickness of ≦300 microns, including but not limited tothicknesses of, for example, 10-50 microns, 50-100 microns, 100-150microns, 150-300 microns, 300, 250, 200 190, 180, 170, 160, 150 140,130, 120 110 100, 90, 80, 70, 60, 50, 40 30, 20, or 10, microns) havinga thickness 28, and a surface modification layer 30 having a thickness38. The glass article 2 is designed to allow the processing of thinsheet 20 in equipment designed for thicker sheets (i.e., those on theorder of ≧0.4 mm, e.g., 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm,or 1.0 mm) although the thin sheet 20 itself is ≦300 microns. That is,the thickness 8, which is the sum of thicknesses 18, 28, and 38, isdesigned to be equivalent to that of the thicker sheet for which a pieceof equipment—for example, equipment designed to dispose electronicdevice components onto substrate sheets—was designed to process. Forexample, if the processing equipment was designed for a 700 micronsheet, and the thin sheet had a thickness 28 of 300 microns, thenthickness 18 would be selected as 400 microns, assuming that thickness38 is negligible. That is, the surface modification layer 30 is notshown to scale; instead, it is greatly exaggerated for sake ofillustration only. Additionally, the surface modification layer is shownin cut-away. In actuality, the surface modification layer would bedisposed uniformly over the bonding surface 14 when providing a reusablecarrier. Typically, thickness 38 will be on the order of nanometers, forexample 0.1 to 2.0, or up to 10 nm, and in some instances may be up to100 nm. The thickness 38 may be measured by ellipsometer. Additionally,the presence of a surface modification layer may be detected by surfacechemistry analysis, for example by ToF Sims mass spectrometry.Accordingly, the contribution of thickness 38 to the article thickness 8is negligible and may be ignored in the calculation for determining asuitable thickness 18 of carrier 10 for processing a given thin sheet 20having a thickness 28. However, to the extent that surface modificationlayer 30 has any significant thickness 38, such may be accounted for indetermining the thickness 18 of a carrier 10 for a given thickness 28 ofthin sheet 20, and a given thickness for which the processing equipmentwas designed.

Carrier 10 has a first surface 12, a bonding surface 14, a perimeter 16,and thickness 18. Further, the carrier 10 may be of any suitablematerial including glass, for example. The carrier need not be glass,but instead can be ceramic, glass-ceramic, or metal (as the surfaceenergy and/or bonding may be controlled in a manner similar to thatdescribed below in connection with a glass carrier). If made of glass,carrier 10 may be of any suitable composition includingalumino-silicate, boro-silicate, alumino-boro-silicate,soda-lime-silicate, and may be either alkali containing or alkali-freedepending upon its ultimate application. Thickness 18 may be from about0.2 to 3 mm, or greater, for example 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7,1.0, 2.0, or 3 mm, or greater, and will depend upon the thickness 28,and thickness 38 when such is non-negligible, as noted above.Additionally, the carrier 10 may be made of one layer, as shown, ormultiple layers (including multiple thin sheets) that are bondedtogether. Further, the carrier may be of a Gen 1 size or larger, forexample, Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 or larger (e.g., sheet sizesfrom 100 mm×100 mm to 3 meters×3 meters or greater).

The thin sheet 20 has a first surface 22, a bonding surface 24, aperimeter 26, and thickness 28. Perimeters 16 and 26 may be of anysuitable shape, may be the same as one another, or may be different fromone another. Further, the thin sheet 20 may be of any suitable materialincluding glass, ceramic, or glass-ceramic, for example. When made ofglass, thin sheet 20 may be of any suitable composition, includingalumino-silicate, boro-silicate, alumino-boro-silicate,soda-lime-silicate, and may be either alkali containing or alkali freedepending upon its ultimate application. The coefficient of thermalexpansion of the thin sheet could be matched relatively closely withthat of the carrier to prevent warping of the article during processingat elevated temperatures. The thickness 28 of the thin sheet 20 is 300microns or less, as noted above. Further, the thin sheet may be of a Gen1 size or larger, for example, Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 orlarger (e.g., sheet sizes from 100 mm×100 mm to 3 meters×3 meters orgreater).

Not only does the article 2 need to have the correct thickness to beprocessed in the existing equipment, it will also need to be able tosurvive the harsh environment in which the processing takes place. Forexample, flat panel display (FPD) processing may include wet ultrasonic,vacuum, and high temperature (e.g., ≧400° C.), processing. For someprocesses, as noted above, the temperature may be ≧500° C., or ≧600° C.,and up to 650° C.

In order to survive the harsh environment in which article 2 will beprocessed, as during FPD manufacture for example, the bonding surface 14should be bonded to bonding surface 24 with sufficient strength so thatthe thin sheet 20 does not separate from carrier 10. And this strengthshould be maintained through the processing so that the thin sheet 20does not separate from the carrier 10 during processing. Further, toallow the thin sheet 20 to be removed from carrier 10 (so that carrier10 may be reused), the bonding surface 14 should not be bonded tobonding surface 24 too strongly either by the initially designed bondingforce, and/or by a bonding force that results from a modification of theinitially designed bonding force as may occur, for example, when thearticle undergoes processing at high temperatures, e.g., temperatures of≧400° C. The surface modification layer 30 may be used to control thestrength of bonding between bonding surface 14 and bonding surface 24 soas to achieve both of these objectives. The controlled bonding force isachieved by controlling the contributions of van der Waals (and/orhydrogen bonding) and covalent attractive energies to the total adhesionenergy which is controlled by modulating the polar and non-polar surfaceenergy components of the thin sheet 20 and the carrier 10. Thiscontrolled bonding is strong enough to survive FPD processing (includingwet, ultrasonic, vacuum, and thermal processes includingtemperatures≧400° C., and in some instances, processing temperatures of≧500° C., or ≧600° C., and up to 650° C.) and remain de-bondable byapplication of sufficient separation force and yet by a force that willnot cause catastrophic damage to the thin sheet 20 and/or the carrier10. Such de-bonding permits removal of thin sheet 20 and the devicesfabricated thereon, and also allows for re-use of the carrier 10.

Although the surface modification layer 30 is shown as a solid layerbetween thin sheet 20 and carrier 10, such need not be the case. Forexample, the layer 30 may be on the order of 0.1 to 2 nm thick, and maynot completely cover every bit of the bonding surface 14. For example,the coverage may be ≦100%, from 1% to 100%, from 10% to 100%, from 20%to 90%, or from 50% to 90%. In other embodiments, the layer 30 may be upto 10 nm thick, or in other embodiments even up to 100 nm thick. Thesurface modification layer 30 may be considered to be disposed betweenthe carrier 10 and thin sheet 20 even though it may not contact one orthe other of the carrier 10 and thin sheet 20. In any event, animportant aspect of the surface modification layer 30 is that itmodifies the ability of the bonding surface 14 to bond with bondingsurface 24, thereby controlling the strength of the bond between thecarrier 10 and the thin sheet 20. The material and thickness of thesurface modification layer 30, as well as the treatment of the bondingsurfaces 14, 24 prior to bonding, can be used to control the strength ofthe bond (energy of adhesion) between carrier 10 and thin sheet 20.

In general, the energy of adhesion between two surfaces is given by (“Atheory for the estimation of surface and interfacial energies. I.derivation and application to interfacial tension”, L. A. Girifalco andR. J. Good, J. Phys. Chem., V 61, p 904):

W=γ ₁+γ₂−γ₁₂  (1)

where •γ₁, γ₂ and γ₁₂ are the surface energies of surface 1, surface 2and the interfacial energy of surface 1 and 2 respectively. Theindividual surface energies are usually a combination of two terms; adispersion component γ^(d), and a polar component γ^(p)

γ=γ^(d)+γ^(p)  (2)

When the adhesion is mostly due to London dispersion forces (γ^(d)) andpolar forces for example hydrogen bonding (γ^(p)), the interfacialenergy could be given by (Girifalco and R. J. Good, as mentioned above):

γ₁₂=γ₁+γ₂−2√{square root over (γ₁ ^(d)γ₂ ^(d))}−2√{square root over (γ₁^(p)γ₂ ^(p))}  (3)

After substituting (3) in (1), the energy of adhesion could beapproximately calculated as:

W˜2[└√{square root over (γ₁ ^(d)γ₂ ^(d))}+√{square root over (γ₁ ^(p)γ₂^(p))}]  (4)

In the above equation (4), only van der Waal (and/or hydrogen bonding)components of adhesion energies are considered. These includepolar-polar interaction (Keesom), polar-non polar interaction (Debye)and nonpolar-nonpolar interaction (London). However, other attractiveenergies may also be present, for example covalent bonding andelectrostatic bonding. So, in a more generalized form, the aboveequation is written as:

W˜2[√{square root over (γ₁ ^(d)γ₂ ^(d))}+√{square root over (γ₁ ^(p)γ₂^(p))}]+w _(c) +w _(e)  (5)

where w_(c) and w_(e) are the covalent and electrostatic adhesionenergies. The covalent adhesion energy is rather common, as in siliconwafer bonding where an initially hydrogen bonded pair of wafers areheated to a higher temperature to convert much or all thesilanol-silanol hydrogen bonds to Si—O—Si covalent bonds. While theinitial, room temperature, hydrogen bonding produces an adhesion energyof the order of ˜100-200 mJ/m² which allows separation of the bondedsurfaces, a fully covalently bonded wafer pair as achieved during hightemperature processing (on the order of 400 to 800° C.) has adhesionenergy of ˜1000-3000 mJ/m² which does not allow separation of the bondedsurfaces; instead, the two wafers act as a monolith. On the other hand,if both the surfaces are perfectly coated with a low surface energymaterial, for example a fluoropolymer, with thickness large enough toshield the effect of the underlying substrate, the adhesion energy wouldbe that of the coating material, and would be very low leading to low orno adhesion between the bonding surfaces 14, 24, whereby the thin sheet20 would not be able to be processed on carrier 10. Consider two extremecases: (a) two standard clean 1 (SC1, as known in the art) cleaned glasssurfaces saturated with silanol groups bonded together at roomtemperature via hydrogen bonding (whereby the adhesion energy is˜100-200 mJ/m²) followed by heating to high temperature which convertsthe silanol groups to covalent Si—O—Si bonds (whereby the adhesionenergy becomes 1000-3000 mJ/m²). This latter adhesion energy is too highfor the pair of glass surfaces to be detachable; and (b) two glasssurfaces perfectly coated with a fluoropolymer with low surface adhesionenergy (˜12 mJ/m² per surface) bonded at room temperature and heated tohigh temperature. In this latter case (b), not only do the surfaces notbond (because the total adhesion energy of ˜24 mJ/m², when the surfacesare put together, is too low), they do not bond at high temperatureeither as there are no (or too few) polar reacting groups. Between thesetwo extremes, a range of adhesion energies exist, for example between50-1000 mJ/m², which can produce the desired degree of controlledbonding. Accordingly, the inventors have found various manners ofproviding a surface modification layer 30 leading to an adhesion energythat is between these two extremes, and such that there can be produceda controlled bonding that is sufficient enough to maintain a pair ofglass substrates (for example a glass carrier 10 and a thin glass sheet20) bonded to one another through the rigors of FPD processing but alsoof a degree that (even after high temperature processing of, e.g. ≧400°C.) allows the detachment of the thin sheet 20 from the carrier 10 afterprocessing is complete. Moreover, the detachment of the thin sheet 20from the carrier 10 can be performed by mechanical forces, and in such amanner that there is no catastrophic damage to at least the thin sheet20, and preferably also so that there is no catastrophic damage to thecarrier 10.

Equation (5) describes that the adhesion energy is a function of foursurface energy parameters plus the covalent and electrostatic energy, ifany.

An appropriate adhesion energy can be achieved by judicious choice ofsurface modifiers, i.e., of surface modification layer 30, and/orthermal treatment of the surfaces prior to bonding. The appropriateadhesion energy may be attained by the choice of chemical modifiers ofeither one or both of bonding surface 14 and bonding surface 24, whichin turn control both the van der Waal (and/or hydrogen bonding, as theseterms are used interchangeably throughout the specification) adhesionenergy as well as the likely covalent bonding adhesion energy resultingfrom high temperature processing (e.g., on the order of ≧400° C.). Forexample, taking a bonding surface of SC1 cleaned glass (that isinitially saturated with silanol groups with high polar component ofsurface energy), and coating it with a low energy fluoropolymer providesa control of the fractional coverage of the surface by polar andnon-polar groups. This not only offers control of the initial van derWaals (and/or hydrogen) bonding at room temperature, but also providescontrol of the extent/degree of covalent bonding at higher temperature.Control of the initial van der Waals (and/or hydrogen) bonding at roomtemperature is performed so as to provide a bond of one surface to theother to allow vacuum and or spin-rinse-dry (SRD) type processing, andin some instances also an easily formed bond of one surface to theother—wherein the easily formed bond can be performed at roomtemperature without application of externally applied forces over theentire area of the thin sheet 20 as is done in pressing the thin sheet20 to the carrier 10 with a squeegee, or with a reduced pressureenvironment. That is, the initial van der Waals bonding provides atleast a minimum degree of bonding holding the thin sheet and carriertogether so that they do not separate if one is held and the other isallowed to be subjected to the force of gravity. In most cases, theinitial van der Walls (and/or hydrogen) bonding will be of such anextent that the article may also go through vacuum, SRD, and ultrasonicprocessing without the thin sheet delaminating from the carrier. Thisprecise control of both van der Waal (and/or hydrogen bonding) andcovalent interactions at appropriate levels via surface modificationlayer 30 (including the materials from which it is made and/or thesurface treatment of the surface to which it is applied), and/or by heattreatment of the bonding surfaces prior to bonding them together,achieves the desired adhesion energy that allows thin sheet 20 to bondwith carrier 10 throughout FPD style processing, while at the same time,allowing the thin sheet 20 to be separated (by an appropriate forceavoiding damage to the thin sheet 20 and/or carrier) from the carrier 10after FPD style processing. In addition, in appropriate circumstances,electrostatic charge could be applied to one or both glass surfaces toprovide another level of control of the adhesion energy.

FPD processing for example p-Si and oxide TFT fabrication typicallyinvolve thermal processes at temperatures above 400° C., above 500° C.,and in some instances at or above 600° C., up to 650° C. which wouldcause glass to glass bonding of a thin glass sheet 20 with a glasscarrier 10 in the absence of surface modification layer 30. Thereforecontrolling the formation of Si—O—Si bonding leads to a reusablecarrier. One method of controlling the formation of Si—O—Si bonding atelevated temperature is to reduce the concentration of surface hydroxylson the surfaces to be bonded.

As shown in FIG. 3, which is Iler's plot (R. K. filer: The Chemistry ofSilica (Wiley-Interscience, New York, 1979) of surface hydroxylconcentration on silica as a function of temperature, the number ofhydroxyls (OH groups) per square nm decreases as the temperature of thesurface increases. Thus, heating a silica surface (and by analogy aglass surface, for example bonding surface 14 and/or bonding surface 24)reduces the concentration of surface hydroxyls, decreasing theprobability that hydroxyls on two glass surfaces will interact. Thisreduction of surface hydroxyl concentration in turn reduces the Si—O—Sibonds formed per unit area, lowering the adhesive force. However,eliminating surface hydroxyls requires long annealing times at hightemperatures (above 750° C. to completely eliminate surface hydroxyls).Such long annealing times and high annealing temperatures result in anexpensive process, and one which is not practical as it is likely to beabove the strain point of typical display glass.

From the above analysis, the inventors have found that an articleincluding a thin sheet and a carrier, suitable for FPD processing(including LTPS processing), can be made by balancing the followingthree concepts:

(1) Modification of the carrier and/or thin sheet bonding surface(s), bycontrolling initial room temperature bonding, which can be done bycontrolling van der Waals (and/or hydrogen) bonding, to create amoderate adhesion energy (for example, having a surface energy of >40mJ/m² per surface prior to the surfaces being bonded) to facilitateinitial room temperature bonding, and sufficient to survivenon-high-temperature FPD processes, for example, vacuum processing, SRDprocessing, and/or ultrasonic processing;

(2) Surface modification of a carrier and/or a thin sheet in a mannerthat is thermally stable to survive FPD processes without outgassingwhich can cause delamination and/or unacceptable contamination in thedevice fabrication, for example, contamination unacceptable to thesemiconductor and/or display making processes in which the article maybe used; and

(3) Controlling bonding at high temperatures, which can be done bycontrolling the carrier surface hydroxyl concentration, andconcentration of other species capable of forming strong covalent bondsat elevated temperatures (e.g., temperature≧400° C.), whereby there canbe controlled the bonding energy between the bonding surfaces of thecarrier and the thin sheet such that even after high temperatureprocessing (especially through thermal processes in the range of500-650° C., as in FPD processes) the adhesive force between the carrierand thin sheet remains within a range that allows debonding of the thinsheet from the carrier with a separation force that does not damage atleast the thin sheet (and preferably that does not damage either thethin sheet or the carrier), and yet sufficient enough to maintain thebond between the carrier and thin sheet so that they do not delaminateduring processing.

Further, the inventors have found that the use of a surface modificationlayer 30, together with bonding surface preparation as appropriate, canbalance the above concepts so as readily to achieve a controlled bondingarea, that is, a bonding area that provides a sufficientroom-temperature bond between the thin sheet 20 and carrier 10 to allowthe article 2 to be processed in FPD type processes (including vacuumand wet processes), and yet one that controls covalent bonding betweenthe thin sheet 20 and carrier 10 (even at elevated temperatures≧400° C.)so as to allow the thin sheet 20 to be removed from the carrier 10(without damage to at least the thin sheet, and preferably withoutdamage to the carrier also) after the article 2 has finished hightemperature processing, for example, FPD type processing or LTPSprocessing. To evaluate potential bonding surface preparations, andsurface modification layers, that would provide a reusable carriersuitable for FPD processing, a series of tests were used to evaluate thesuitability of each. Different FPD applications have differentrequirements, but LTPS and Oxide TFT processes appear to be the moststringent at this time and, thus, tests representative of steps in theseprocesses were chosen, as these are desired applications for the article2. Vacuum processes, wet cleaning (including SRD and ultrasonic typeprocesses) and wet etching are common to many FPD applications. TypicalaSi TFT fabrication requires processing up to 320° C. Annealing at 400°C. is used in oxide TFT processes, whereas crystallization and dopantactivation steps over 600° C. are used in LTPS processing. Accordingly,the following five tests were used to evaluate the likelihood that aparticular bonding surface preparation and surface modification layer 30would allow a thin sheet 20 to remain bonded to a carrier 10 throughoutFPD processing, while allowing the thin sheet 20 to be removed from thecarrier 10 (without damaging the thin sheet 20 and/or the carrier 10)after such processing (including processing at temperatures≧400° C.).The tests were performed in order, and a sample progressed from one testto the next unless there was failure of the type that would not permitthe subsequent testing.

(1) Vacuum testing. Vacuum compatibility testing was performed in an STSMultiplex PECVD loadlock (available from SPTS, Newport, UK)—The loadlockwas pumped by an Ebara A10S dry pump with a soft pump valve (availablefrom Ebara Technologies Inc., Sacramento, Calif. A sample was placed inthe loadlock, and then the loadlock was pumped from atmospheric pressuredown to 70 mTorr in 45 sec. Failure, indicated by a notation of “F” inthe “Vacuum” column of the tables below, was deemed to have occurred ifthere was: (a) a loss of adhesion between the carrier and the thin sheet(by visual inspection with the naked eye, wherein failure was deemed tohave occurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) movement ofthe thin sheet relative to the carrier (as determined by visualobservation with the naked eye—samples were photographed before andafter testing, wherein failure was deemed to have occurred if there wasa movement of bond defects, e.g., bubbles, or if edges debonded, or ifthere was a movement of the thin sheet on the carrier). In the tablesbelow, a notation of “P” in the “Vacuum” column indicates that thesample did not fail as per the foregoing criteria.

(2) Wet process testing. Wet processes compatibility testing wasperformed using a Semitool model SRD-470S (available from AppliedMaterials, Santa Clara, Calif.). The testing consisted of 60 seconds 500rpm rinse, Q-rinse to 15 MOhm-cm at 500 rpm, 10 seconds purge at 500rpm, 90 seconds dry at 1800 rpm, and 180 seconds dry at 2400 rpm underwarm flowing nitrogen. Failure, as indicated by a notation of “F” in the“SRD” column of the tables below, was deemed to have occurred if therewas: (a) a loss of adhesion between the carrier and the thin sheet (byvisual inspection with the naked eye, wherein failure was deemed to haveoccurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) movement ofthe thin sheet relative to the carrier (as determined by visualobservation with the naked eye—samples were photographed before andafter testing, wherein failure was deemed to have occurred if there wasa movement of bond defects, e.g., bubbles, or if edges debonded, or ifthere was a movement of the thin sheet on the carrier); or (d)penetration of water under the thin sheet (as determined by visualinspection with an optical microscope at 50×, wherein failure wasdetermined to have occurred if liquid or residue was observable). In thetables below, a notation of “P” in the “SRD” column indicates that thesample did not fail as per the foregoing criteria.

(3) Temperature to 400° C. testing. 400° C. process compatibilitytesting was performed using an Alwin21 Accuthermo610 RTP (available fromAlwin21, Santa Clara Calif. A carrier with a thin sheet bonded theretowas heated in a chamber cycled from room temperature to 400° C. at 6.2°C./min, held at 400° C. for 600 seconds, and cooled at 1° C./min to 300°C. The carrier and thin sheet were then allowed to cool to roomtemperature. Failure, as indicated by a notation of “F” in the “400° C.”column of the tables below, was deemed to have occurred if there was:(a) a loss of adhesion between the carrier and the thin sheet (by visualinspection with the naked eye, wherein failure was deemed to haveoccurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) increasedadhesion between the carrier and the thin sheet whereby such increasedadhesion prevents debonding (by insertion of a razor blade between thethin sheet and carrier, and/or by sticking a piece of Kapton™ tape, 1″wide×6″ long with 2-3″ attached to 100 mm square thin glass (K102 seriesfrom Saint Gobain Performance Plastic, Hoosik N.Y.) to the thin sheetand pulling on the tape) of the thin sheet from the carrier withoutdamaging the thin sheet or the carrier, wherein a failure was deemed tohave occurred if there was damage to the thin sheet or carrier uponattempting to separate them, or if the thin sheet and carrier could notbe debonded by performance of either of the debonding methods.Additionally, after the thin sheet was bonded with the carrier, andprior to the thermal cycling, debonding tests were performed onrepresentative samples to determine that a particular material,including any associated surface treatment, did allow for debonding ofthe thin sheet from the carrier prior to the temperature cycling. In thetables below, a notation of “P” in the “400° C.” column indicates thatthe sample did not fail as per the foregoing criteria.

(4) Temperature to 600° C. testing. 600° C. process compatibilitytesting was performed using an Alwin21 Accuthermo610 RTP. A carrier witha thin sheet was heated in a chamber cycled from room temperature to600° C. at 9.5° C./min, held at 600° C. for 600 seconds, and then cooledat 1° C./min to 300° C. The carrier and thin sheet were then allowed tocool to room temperature. Failure, as indicated by a notation of “F” inthe “600° C.” column of the tables below, was deemed to have occurred ifthere was: (a) a loss of adhesion between the carrier and the thin sheet(by visual inspection with the naked eye, wherein failure was deemed tohave occurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) increasedadhesion between the carrier and the thin sheet whereby such increasedadhesion prevents debonding (by insertion of a razor blade between thethin sheet and carrier, and/or by sticking a piece of Kapton™ tape asdescribed above to the thin sheet and pulling on the tape) of the thinsheet from the carrier without damaging the thin sheet or the carrier,wherein a failure was deemed to have occurred if there was damage to thethin sheet or carrier upon attempting to separate them, or if the thinsheet and carrier could not be debonded by performance of either of thedebonding methods. Additionally, after the thin sheet was bonded withthe carrier, and prior to the thermal cycling, debonding tests wereperformed on representative samples to determine that a particularmaterial, and any associated surface treatment, did allow for debondingof the thin sheet from the carrier prior to the temperature cycling. Inthe tables below, a notation of “P” in the “600° C.” column indicatesthat the sample did not fail as per the foregoing criteria.

(5) Ultrasonic testing. Ultrasonic compatibility testing was performedby cleaning the article in a four tank line, wherein the article wasprocessed in each of the tanks sequentially from tank #1 to tank #4.Tank dimensions, for each of the four tanks, were 18.4″L×10″W×15″D. Twocleaning tanks (#1 and #2) contained 1% Semiclean KG available fromYokohama Oils and Fats Industry Co Ltd., Yokohama Japan in DI water at50° C. The cleaning tank #1 was agitated with a NEY prosonik 2 104 kHzultrasonic generator (available from Blackstone-NEY Ultrasonics,Jamestown, N.Y.), and the cleaning tank #2 was agitated with a NEYprosonik 2 104 kHz ultrasonic generator. Two rinse tanks (tank #3 andtank #4) contained DI water at 50° C. The rinse tank #3 was agitated byNEY sweepsonik 2D 72 kHz ultrasonic generator and the rinse tank #4 wasagitated by a NEY sweepsonik 2D 104 kHz ultrasonic generator. Theprocesses were carried out for 10 min in each of the tanks #1-4,followed by spin rinse drying (SRD) after the sample was removed fromtank #4. Failure, as indicated by a notation of “F” in the “Ultrasonic”column of the tables below, was deemed to have occurred if there was:(a) a loss of adhesion between the carrier and the thin sheet (by visualinspection with the naked eye, wherein failure was deemed to haveoccurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) formation ofother gross defects (as determined by visual inspection with opticalmicroscope at 50×, wherein failure was deemed to have occurred if therewere particles trapped between the thin glass and carrier that were notobserved before; or (d) penetration of water under the thin sheet (asdetermined by visual inspection with an optical microscope at 50×,wherein failure was determined to have occurred if liquid or residue wasobservable. In the tables below, a notation of “P” in the “Ultrasonic”column indicates that the sample did not fail as per the foregoingcriteria. Additionally, in the tables below, a blank or a “?” in the“Ultrasonic” column indicates that the sample was not tested in thismanner.

Preparation of Bonding Surfaces Via Hydroxyl Reduction by Heating

The benefit of modifying one or more of the bonding surfaces 14, 24 witha surface modification layer 30 so the article 2 is capable ofsuccessfully undergoing FPD processing (i.e., where the thin sheet 20remains bonded to the carrier 10 during processing, and yet may beseparated from the carrier 10 after processing, including hightemperature processing) was demonstrated by processing articles 2 havingglass carriers 10 and thin glass sheets 20 without a surfacemodification layer 30 therebetween. Specifically, first there was triedpreparation of the bonding surfaces 14, 24 by heating to reduce hydroxylgroups, but without a surface modification layer 30. The carriers 10 andthin sheets 20 were cleaned, the bonding surfaces 14 and 24 were bondedto one another, and then the articles 2 were tested. A typical cleaningprocess for preparing glass for bonding is the SC1 cleaning processwhere the glass is cleaned in a dilute hydrogen peroxide and base(commonly ammonium hydroxide, but tetramethylammonium hydroxidesolutions for example JT Baker JTB-100 or JTB-111 may also be used).Cleaning removes particles from the bonding surfaces, and makes thesurface energy known, i.e., it provides a base-line of surface energy.The manner of cleaning need not be SC1, other types of cleaning may beused, as the type of cleaning is likely to have only a very minor effecton the silanol groups on the surface. The results for various tests areset forth below in Table 1.

A strong but separable initial, room temperature or van der Waal and/orHydrogen-bond was created by simply cleaning a thin glass sheet of 100mm square×100 micron thick, and a glass carrier 150 mm diameter singlemean flat (SMF) wafer 0.50 or 0.63 mm thick, each comprising Eagle XG®display glass (an alkali-free, alumino-boro-silicate glass, having anaverage surface roughness Ra on the order of 0.2 nm, available fromCorning Incorporated, Corning, N.Y.). In this example, glass was cleaned10 min in a 65° C. bath of 40:1:2 DI water: JTB-111:Hydrogen peroxide.The thin glass or glass carrier may or may not have been annealed innitrogen for 10 min at 400° C. to remove residual water—the notation“400° C.” in the “Carrier” column or the “Thin Glass” column in Table 1below indicates that the sample was annealed in nitrogen for 10 minutesat 400° C. FPD process compatibility testing demonstrates this SC1-SC1initial, room temperature, bond is mechanically strong enough to passvacuum, SRD and ultrasonic testing. However, heating at 400° C. andabove created a permanent bond between the thin glass and carrier, i.e.,the thin glass sheet could not be removed from the carrier withoutdamaging either one or both of the thin glass sheets and carrier. Andthis was the case even for Example 1c, wherein each of the carrier andthe thin glass had an annealing step to reduce the concentration ofsurface hydroxyls. Accordingly, the above-described preparation of thebonding surfaces 14, 24 via heating alone and then bonding of thecarrier 10 and the thin sheet 12, without a surface modification layer30, is not a suitable controlled bond for FPD processes wherein thetemperature will be ≧400° C.

TABLE 1 process compatibility testing of SC1-treated glass bondingsurfaces Example Carrier Thin Glass Vacuum SRD 400 C. 600 C. Ultrasonic1a SC1 SC1 P P F F P 1b SC1, 400 C. SC1 P P F F P 1c SC1, 400 C. SC1,400 C. P P F F P

Preparation of Bonding Surfaces by Hydroxyl Reduction and SurfaceModification Layer

Hydroxyl reduction, as by heat treatment for example, and a surfacemodification layer 30 may be used together to control the interaction ofbonding surfaces 14, 24. For example, the bonding energy (both van derWaals and/or Hydrogen-bonding at room temperature due to thepolar/dispersion energy components, and covalent bonding at hightemperature due to the covalent energy component) of the bondingsurfaces 14, 24 can be controlled so as to provide varying bond strengthfrom that wherein room-temperature bonding is difficult, to thatallowing easy room-temperature bonding and separation of the bondingsurfaces after high temperature processing, to that which—after hightemperature processing—prevents the surfaces from separating withoutdamage. In some applications, it may be desirable to have no, or veryweak bonding (as when the surfaces are in a “non-bonding” region, as a“non-bonding” region is described in the thin sheet/carrier concept ofUS '727, and as described below). In other applications, for exampleproviding a re-usable carrier for FPD processes and the like (whereinprocess temperatures≧500° C., or ≧600° C., and up to 650° C., may beachieved), it is desirable to have sufficient van der Waals and/orHydrogen-bonding, at room temperature to initially put the thin sheetand carrier together, and yet prevent or limit high temperature covalentbonding. For still other applications, it may be desirable to havesufficient room temperature boding to initially put the thin sheet andcarrier together, and also to develop strong covalent bonding at hightemperature (as when the surfaces are in a “bonding region”, as “bondingregion” is described in the thin sheet/carrier concept of US '727, andas discussed below). Although not wishing to be bound by theory, in someinstances the surface modification layer may be used to control roomtemperature bonding by which the thin sheet and carrier are initiallyput together, whereas the reduction of hydroxyl groups on the surface(as by heating the surface, or by reaction of the hydroxyl groups withthe surface modification layer, for example) may be used to control thecovalent bonding, particularly that at high temperatures.

A material for the surface modification layer 30 may provide a bondingsurface 14, 24 with an energy (for example, and energy<40 mJ/m², asmeasured for one surface, and including polar and dispersion components)whereby the surface produces only weak bonding. In one example,hexamethyldisilazane (HMDS) may be used to create this low energysurface by reacting with the surface hydroxyls to leave a trimethylsilyl(TMS) terminated surface. HMDS as a surface modification layer may beused together with surface heating to reduce the hydroxyl concentrationto control both room temperature and high temperature bonding. Bychoosing a suitable bonding surface preparation for each bonding surface14, 24, there can be achieved articles having a range of capabilities.More specifically, of interest to providing a reusable carrier for LTPSprocessing, there can be achieved a suitable bond between a thin glasssheet 20 and a glass carrier 10 so as to survive (or pass) each of thevacuum SRD, 400° C. (parts a and c), and 600° C. (parts a and c),processing tests.

In one example, following SC1 cleaning by HMDS treatment of both thinglass and carrier creates a weakly bonded surface which is challengingto bond at room temperature with van der Waals (and/or hydrogen bonding)forces. Mechanical force is applied to bond the thin glass to thecarrier. As shown in example 2a of Table 2, this bonding is sufficientlyweak that deflection of the carrier is observed in vacuum testing andSRD processing, bubbling (likely due to outgassing) was observed in 400°C. and 600° C. thermal processes, and particulate defects were observedafter ultrasonic processing.

In another example, HMDS treatment of just one surface (carrier in theexample cited) creates stronger room temperature adhesion which survivesvacuum and SRD processing. However, thermal processes at 400° C. andabove permanently bonded the thin glass to the carrier. This is notunexpected as the maximum surface coverage of the trimethylsilyl groupson silica has been calculated by Sindorf and Maciel in J. Phys. Chem.1982, 86, 5208-5219 to be 2.8/nm² and measured by Suratwala et. al. inJournal of Non-Crystalline Solids 316 (2003) 349-363 as 2.7/nm², vs. ahydroxyl concentration of 4.6-4.9/nm² for fully hydroxylated silica.That is, although the trimethylsilyl groups do bond with some surfacehydroxyls, there will remain some un-bonded hydroxyls. Thus one wouldexpect condensation of surface silanol groups to permanently bond thethin glass and carrier given sufficient time and temperature.

A varied surface energy can be created by heating the glass surface toreduce the surface hydroxyl concentration prior to HMDS exposure,leading to an increased polar component of the surface energy. This bothdecreases the driving force for formation of covalent Si—O—Si bonds athigh temperature and leads to stronger room-temperature bonding, forexample, van der Waal (and/or hydrogen) bonding. FIG. 4 shows thesurface energy of an Eagle XG® display glass carrier after annealing,and after HMDS treatment. Increased annealing temperature prior to HMDSexposure increases the total (polar and dispersion) surface energy (line402) after HMDS exposure by increasing the polar contribution (line404). It is also seen that the dispersion contribution (line 406) to thetotal surface energy remains largely unchanged by the heat treatment.Although not wishing to be bound by theory, increasing the polarcomponent of, and thereby the total, energy in the surface after HMDStreatment appears to be due to there being some exposed glass surfaceareas even after HMDS treatment because of sub-monolayer TMS coverage bythe HMDS.

In example 2b, the thin glass sheet was heated at a temperature of 150°C. in a vacuum for one hour prior to bonding with the non-heat-treatedcarrier having a coating of HMDS. This heat treatment of the thin glasssheet was not sufficient to prevent permanent bonding of the thin glasssheet to the carrier at temperatures≧400° C.

As shown in examples 2c-2e of Table 2, varying the annealing temperatureof the glass surface prior to HMDS exposure can vary the bonding energyof the glass surface so as to control bonding between the glass carrierand the thin glass sheet.

In example 2c, the carrier was annealed at a temperature of 190° C. invacuum for 1 hour, followed by HMDS exposure to provide surfacemodification layer 30. Additionally, the thin glass sheet was annealedat 450° C. in a vacuum for 1 hour before bonding with the carrier. Theresulting article survived the vacuum, SRD, and 400° C. tests (parts aand c, but did not pass part b as there was increased bubbling), butfailed the 600° C. test. Accordingly, although there was increasedresistance to high temperature bonding as compared with example 2b, thiswas not sufficient to produce an article for processing attemperatures≧600° C. (for example LTPS processing) wherein the carrieris reusable.

In example 2d, the carrier was annealed at a temperature of 340° C. in avacuum for 1 hour, followed by HMDS exposure to provide surfacemodification layer 30. Again, the thin glass sheet was annealed at 450°C. for 1 hour in a vacuum before bonding with the carrier. The resultswere similar to those for example 2c, wherein the article survived thevacuum, SRD, and 400° C. tests (parts a and c, but did not pass part bas there was increased bubbling), but failed the 600° C. test.

As shown in example 2e, annealing both thin glass and carrier at 450° C.in vacuum for 1 hr, followed by HMDS exposure of the carrier, and thenbonding of the carrier and thin glass sheet, improves the temperatureresistance to permanent bonding. An anneal of both surfaces to 450° C.prevents permanent bonding after RTP annealing at 600° C. for 10 min,that is, this sample passed the 600° C. processing test (parts a and c,but did not pass part b as there was increased bubbling; a similarresult was found for the 400° C. test).

TABLE 2 process compatibility testing of HMDS surface modificationlayers Example Carrier Thin Glass Vacuum SRD 400 C. 600 C. Ultrasonic 2aSC1, HMDS SC1, HMDS F F P P F 2b SC1, HMDS SC1, 150 C. P P F F 2c SC1,190 C., HMDS SC1, 450 C. P P P F 2d SC1, 340 C., HMDS SC1, 450 C. P P PF 2e SC1, 450 C., HMDS SC1, 450 C. P P P P

In Examples 2a to 2e above, each of the carrier and the thin sheet wereEagle XG® glass, wherein the carrier was a 150 mm diameter SMF wafer 630microns thick and the thin sheet was 100 mm square 100 microns thick TheHMDS was applied by pulse vapor deposition in a YES-5 HMDS oven(available from Yield Engineering Systems, San Jose Calif.) and was oneatomic layer thick (i.e., about 0.2 to 1 nm), although the surfacecoverage may be less than one monolayer, i.e., some of the surfacehydroxyls are not covered by the HMDS as noted by Maciel and discussedabove. Because of the small thickness in the surface modification layer,there is little risk of outgassing which can cause contamination in thedevice fabrication. Also, as indicated in Table 2 by the “SC1” notation,each of the carriers and thin sheets were cleaned using an SC1 processprior to heat treating or any subsequent HMDS treatment.

A comparison of example 2a with example 2b shows that the bonding energybetween the thin sheet and the carrier can be controlled by varying thenumber of surfaces which include a surface modification layer. Andcontrolling the bonding energy can be used to control the bonding forcebetween two bonding surfaces. Also, a comparison of examples 2b-2e,shows that the bonding energy of a surface can be controlled by varyingthe parameters of a heat treatment to which the bonding surface issubjected before application of a surface modification material. Again,the heat treatment can be used to reduce the number of surface hydroxylsand, thus, control the degree of covalent bonding, especially that athigh temperatures.

Other materials, that may act in a different manner to control thesurface energy on a bonding surface, may be used for the surfacemodification layer 30 so as to control the room temperature and hightemperature bonding forces between two surfaces. For example, a reusablecarrier can also be created if one or both bonding surfaces are modifiedto create a moderate bonding force with a surface modification layerthat either covers, or sterically hinders species for example hydroxylsto prevent the formation at elevated temperature of strong permanentcovalent bonds between carrier and thin sheet. One way to create atunable surface energy, and cover surface hydroxyls to prevent formationof covalent bonds, is deposition of plasma polymer films, for examplefluoropolymer films. Plasma polymerization deposits a thin polymer filmunder atmospheric or reduced pressure and plasma excitation (DC or RFparallel plate, Inductively Coupled Plasma (ICP) Electron CyclotronResonance (ECR) downstream microwave or RF plasma) from source gases forexample fluorocarbon sources (including CF4, CHF3, C2F6, C3F6, C2F2,CH3F, C4F8, chlorofluoro carbons, or hydrochlorofluoro carbons),hydrocarbons for example alkanes (including methane, ethane, propane,butane), alkenes (including ethylene, propylene), alkynes (includingacetylene), and aromatics (including benzene, toluene), hydrogen, andother gas sources for example SF6. Plasma polymerization creates a layerof highly cross-linked material. Control of reaction conditions andsource gases can be used to control the film thickness, density, andchemistry to tailor the functional groups to the desired application.

FIG. 5 shows the total (line 502) surface energy (including polar (line504) and dispersion (line 506) components) of plasma polymerizedfluoropolymer (PPFP) films deposited from CF4-C4F8 mixtures with anOxford ICP380 etch tool (available from Oxford Instruments, OxfordshireUK). The films were deposited onto a sheet of Eagle XG® glass, andspectroscopic ellipsometry showed the films to be 1-10 nm thick. As seenfrom FIG. 5, glass carriers treated with plasma polymerizedfluoropolymer films containing less than 40% C4F8 exhibit a surfaceenergy>40 mJ/m² and produce controlled bonding between the thin glassand carrier at room temperature by van der Waal or hydrogen bonding.Facilitated bonding is observed when initially bonding the carrier andthin glass at room temperature. That is, when placing the thin sheetonto the carrier, and pressing them together at a point, a wave fronttravels across the carrier, but at a lower speed than is observed forSC1 treated surfaces having no surface modification layer thereon. Thecontrolled bonding is sufficient to withstand all standard FPD processesincluding vacuum, wet, ultrasonic, and thermal processes up to 600° C.,that is this controlled bonding passed the 600° C. processing testwithout movement or delamination of the thin glass from the carrier.De-bonding was accomplished by peeling with a razor blade and/or Kapton™tape as described above. The process compatibility of two different PPFPfilms (deposited as described above) is shown in Table 3. PPFP 1 ofexample 3a was formed with C4F8/(C4F8+CF4)=0, that is, formed withCF4/H2 and not C4F8, and PPFP 2 of example 3b was deposited withC4F8/(C4F8+CF4)=0.38. Both types of PPFP films survived the vacuum, SRD,400° C. and 600° C. processing tests. However, delamination is observedafter 20 min of ultrasonic cleaning of PPFP 2 indicating insufficientadhesive force to withstand such processing. Nonetheless, the surfacemodification layer of PPFP2 may be useful for some applications, aswhere ultrasonic processing is not necessary.

TABLE 3 process compatibility testing of PPFP surface modificationlayers Ex- Thin Ultra- ample Carrier Glass Vacuum SRD 400 C. 600 C.sonic 3a PPFP 1 SC1, P P P P P 150 C. 3b PPFP2 SC1, P P P P F 150 C.

In Examples 3a and 3b above, each of the carrier and the thin sheet wereEagle XG® glass, wherein the carrier was a 150 mm diameter SMF wafer 630microns thick and the thin sheet was 100 mm square 100 microns thick.Because of the small thickness in the surface modification layer, thereis little risk of outgassing which can cause contamination in the devicefabrication. Further, because the surface modification layer did notappear to degrade, again, there is even less risk of outgassing. Also,as indicated in Table 3, each of the thin sheets was cleaned using anSC1 process prior to heat treating at 150° C. for one hour in a vacuum.

Still other materials, that may function in a different manner tocontrol surface energy, may be used as the surface modification layer tocontrol the room temperature and high temperature bonding forces betweenthe thin sheet and the carrier. For example, a bonding surface that canproduce controlled bonding can be created by silane treating a glasscarrier and/or glass thin sheet. Silanes are chosen so as to produce asuitable surface energy, and so as to have sufficient thermal stabilityfor the application. The carrier or thin glass to be treated may becleaned by a process for example O2 plasma or UV-ozone, and SC1 orstandard clean two (SC2, as is known in the art) cleaning to removeorganics and other impurities (metals, for example) that would interferewith the silane reacting with the surface silanol groups. Washes basedon other chemistries may also be used, for example, HF, or H2SO4 washchemistries. The carrier or thin glass may be heated to control thesurface hydroxyl concentration prior to silane application (as discussedabove in connection with the surface modification layer of HMDS), and/ormay be heated after silane application to complete silane condensationwith the surface hydroxyls. The concentration of unreacted hydroxylgroups after silanization may be made low enough prior to bonding as toprevent permanent bonding between the thin glass and carrier attemperatures≧400° C., that is, to form a controlled bond. This approachis described below.

Example 4a

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% dodecyltriethoxysilane (DDTS) in toluene, andannealed at 150° C. in vacuum for 1 hr to complete condensation. DDTStreated surfaces exhibit a surface energy of 45 mJ/m². As shown in Table4, a glass thin sheet (having been SC1 cleaned and heated at 400° C. ina vacuum for one hour) was bonded to the carrier bonding surface havingthe DDTS surface modification layer thereon. This article survived wetand vacuum process tests but did not survive thermal processes over 400°C. without bubbles forming under the carrier due to thermaldecomposition of the silane. This thermal decomposition is expected forall linear alkoxy and chloro alkylsilanes R1_(x)Si(OR2)_(y)(Cl)_(z)where x=1 to 3, and y+z=4−x except for methyl, dimethyl, and trimethylsilane (x=1 to 3, R1=CH₃) which produce coatings of good thermalstability.

Example 4b

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% 3,3,3, trifluoropropyltritheoxysilane (TFTS) intoluene, and annealed at 150° C. in vacuum for 1 hr to completecondensation. TFTS treated surfaces exhibit a surface energy of 47mJ/m². As shown in Table 4, a glass thin sheet (having been SC1 cleanedand then heated at 400° C. in a vacuum for one hour) was bonded to thecarrier bonding surface having the TFTS surface modification layerthereon. This article survived the vacuum, SRD, and 400° C. processtests without permanent bonding of the glass thin sheet to the glasscarrier. However, the 600° C. test produced bubbles forming under thecarrier due to thermal decomposition of the silane. This was notunexpected because of the limited thermal stability of the propyl group.Although this sample failed the 600° C. test due to the bubbling, thematerial and heat treatment of this example may be used for someapplications wherein bubbles and the adverse effects thereof, forexample reduction in surface flatness, or increased waviness, can betolerated.

Example 4c

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% phenyltriethoxysilane (PTS) in toluene, andannealed at 200° C. in vacuum for 1 hr to complete condensation. PTStreated surfaces exhibit a surface energy of 54 mJ/m². As shown in Table4, a glass thin sheet (having been SC1 cleaned and then heated at 400°C. in a vacuum for one hour) was bonded to the carrier bonding surfacehaving the PTS surface modification layer. This article survived thevacuum, SRD, and thermal processes up to 600° C. without permanentbonding of the glass thin sheet with the glass carrier.

Example 4d

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% diphenyldiethoxysilane (DPDS) in toluene, andannealed at 200° C. in vacuum for 1 hr to complete condensation. DPDStreated surfaces exhibit a surface energy of 47 mJ/m². As shown in Table4, a glass thin sheet (having been SC1 cleaned and then heated at 400°C. in a vacuum for one hour) was bonded to the carrier bonding surfacehaving the DPDS surface modification layer. This article survived thevacuum and SRD tests, as well as thermal processes up to 600° C. withoutpermanent bonding of the glass thin sheet with the glass carrier

Example 4e

A glass carrier having its bonding surface O2 plasma and SC1 treated wasthen treated with 1% 4-pentafluorophenyltriethoxysilane (PFPTS) intoluene, and annealed at 200° C. in vacuum for 1 hr to completecondensation. PFPTS treated surfaces exhibit a surface energy of 57mJ/m². As shown in Table 4, a glass thin sheet (having been SC1 cleanedand then heated at 400° C. in a vacuum for one hour) was bonded to thecarrier bonding surface having the PFPTS surface modification layer.This article survived the vacuum and SRD tests, as well as thermalprocesses up to 600° C. without permanent bonding of the glass thinsheet with the glass carrier.

TABLE 4 process compatibility testing of silane surface modificationlayers Ex- ample Carrier Thin Glass Vacuum SRD 400 C. 600 C. 4a SC1,DDTS SC1, 400 C. P P F F 4b SC1, TFTS SC1, 400 C. P P P F 4c SC1, PTSSC1, 400 C. P P P P 4d SC1, DPDS SC1, 400 C. P P P P 4e SC1, PFPTS SC1,400 C. P P P P

In Examples 4a to 4e above, each of the carrier and the thin sheet wereEagle XG® glass, wherein the carrier was a 150 mm diameter SMF wafer 630microns thick and the thin sheet was 100 mm square 100 microns thick.The silane layers were self-assembled monolayers (SAM), and thus were onthe order of less than about 2 nm thick. In the above examples, the SAMwas created using an organosilane with an aryl or alkyl non-polar tailand a mono, di, or tri-alkoxide head group. These react with the silnaolsurface on the glass to directly attach the organic functionality.Weaker interactions between the non-polar head groups organize theorganic layer. Because of the small thickness in the surfacemodification layer, there is little risk of outgassing which can causecontamination in the device fabrication. Further, because the surfacemodification layer did not appear to degrade in examples 4c, 4d, and 4e,again, there is even less risk of outgassing. Also, as indicated inTable 4, each of the glass thin sheets was cleaned using an SC1 processprior to heat treating at 400° C. for one hour in a vacuum.

As can be seen from a comparison of examples 4a-4e, controlling surfaceenergy of the bonding surfaces to be above 40 mJ/m² so as to facilitatethe initial room temperature bonding is not the only consideration tocreating a controlled bond that will withstand FPD processing and stillallow the thin sheet to be removed from the carrier without damage.Specifically, as seen from examples 4a-4e, each carrier had a surfaceenergy above 40 mJ/m², which facilitated initial room temperaturebonding so that the article survived vacuum and SRD processing. However,examples 4a and 4b did not pass 600° C. processing test. As noted above,for certain applications, it is also important for the bond to surviveprocessing up to high temperatures (for example, ≧400° C., ≧500° C., or≧600° C., up to 650° C., as appropriate to the processes in which thearticle is designed to be used) without degradation of the bond to thepoint where it is insufficient to hold the thin sheet and carriertogether, and also to control the covalent bonding that occurs at suchhigh temperatures so that there is no permanent bonding between the thinsheet and the carrier.

The above-described separation in examples 4, 3, and 2, is performed atroom temperature without the addition of any further thermal or chemicalenergy to modify the bonding interface between the thin sheet andcarrier. The only energy input is mechanical pulling and/or peelingforce.

The materials described above in examples 3 and 4 can be applied to thecarrier, to the thin sheet, or to both the carrier and thin sheetsurfaces that will be bonded together.

Uses of Controlled Bonding

Reusable Carrier

One use of controlled bonding via surface modification layers (includingmaterials and the associated bonding surface heat treatment) is toprovide reuse of the carrier in an article undergoing processesrequiring a temperature≧600° C., as in LTPS processing, for example.Surface modification layers (including the materials and bonding surfaceheat treatments), as exemplified by the examples 2e, 3a, 3b, 4c, 4d, and4e, above, may be used to provide reuse of the carrier under suchtemperature conditions. Specifically, these surface modification layersmay be used to modify the surface energy of the area of overlap betweenthe bonding areas of the thin sheet and carrier, whereby the entire thinsheet may be separated from the carrier after processing. The thin sheetmay be separated all at once, or may be separated in sections as, forexample, when first removing devices produced on portions of the thinsheet and thereafter removing the remaining portions to clean thecarrier for reuse. In the event that the entire thin sheet is removedfrom the carrier, the carrier can be reused as is by simply by placinganother thin sheet thereon. Alternatively, the carrier may be cleanedand once again prepared to carry a thin sheet by forming a surfacemodification layer anew. Because the surface modification layers preventpermanent bonding of the thin sheet with the carrier, they may be usedfor processes wherein temperatures are ≧600° C. Of course, althoughthese surface modification layers may control bonding surface energyduring processing at temperatures≧600° C., they may also be used toproduce a thin sheet and carrier combination that will withstandprocessing at lower temperatures, and may be used in such lowertemperature applications to control bonding. Moreover, where the thermalprocessing of the article will not exceed 400° C., surface modificationlayers as exemplified by the examples 2c, 2d, 4b may also be used inthis same manner.

To Provide a Controlled Bonding Area

A second use of controlled bonding via surface modification layers(including materials and the associated bonding surface heat treatments)is to provide a controlled bonding area, between a glass carrier and aglass thin sheet. More specifically, with the use of the surfacemodification layers an area of controlled bonding can be formed whereina sufficient separation force can separate the thin sheet portion fromthe carrier without damage to either the thin sheet or the carriercaused by the bond, yet there is maintained throughout processing asufficient bonding force to hold the thin sheet relative to the carrier.With reference to FIG. 6, a glass thin sheet 20 may be bonded to a glasscarrier 10 by a bonded area 40. In the bonded area 40, the carrier 10and thin sheet 20 are covalently bonded to one another so that they actas a monolith. Additionally, there are controlled bonding areas 50having perimeters 52, wherein the carrier 10 and thin sheet 20 areconnected, but may be separated from one another, even after hightemperature processing, e.g. processing at temperatures≧600° C. Althoughten controlled bonding areas 50 are shown in FIG. 6, any suitablenumber, including one, may be provided. The surface modification layers30, including the materials and bonding surface heat treatments, asexemplified by the examples 2a, 2e, 3a, 3b, 4c, 4d, and 4e, above, maybe used to provide the controlled bonding areas 50 between the carrier10 and the thin sheet 20. Specifically, these surface modificationlayers may be formed within the perimeters 52 of controlled bondingareas 50 either on the carrier 10 or on the thin sheet 20. Accordingly,when the article 2 is processed at high temperature, either to formcovalent bonding in the bonding area 40 or during device processing,there can be provided a controlled bond between the carrier 10 and thethin sheet 20 within the areas bounded by perimeters 52 whereby aseparation force may separate (without catastrophic damage to the thinsheet or carrier) the thin sheet and carrier in this region, yet thethin sheet and carrier will not delaminate during processing, includingultrasonic processing. The controlled bonding of the presentapplication, as provided by the surface modification layers and anyassociated heat treatments, is thus able to improve upon the carrierconcept in US '727. Specifically, Although the carriers of US '727 weredemonstrated to survive FPD processing, including high temperatureprocessing≧about 600° C. with their bonded peripheries and non-bondedcenter regions, ultrasonic processes for example wet cleans and resiststrip processing remained challenging. Specifically, pressure waves inthe solution were seen to induce sympathic vibrations in the thin glassin the non-bonding region (as non-bonding was described in US '727), asthere was little or no adhesive force bonding the thin glass and carrierin that region. Standing waves in the thin glass can be formed, whereinthese waves may cause vibrations that can lead to breakage of the thinglass at the interface between the bonded and non-bonded regions if theultrasonic agitation is of sufficient intensity. This problem can beeliminated by minimizing the gap between the thin glass and the carrierand by providing sufficient adhesion, or controlled bonding between thecarrier 20 and thin glass 10 in these areas 50. Surface modificationlayers (including materials and any associated heat treatments asexemplified by examples 2a, 2e, 3a, 3b, 4c, 4d, and 4e) of the bondingsurfaces control the bonding energy so as to provide a sufficient bondbetween the thin sheet 20 and carrier 10 to avoid these unwantedvibrations in the controlled bonding region.

Then, during extraction of the desired parts 56 having perimeters 57,the portions of thin sheet 20 within the perimeters 52 may simply beseparated from the carrier 10 after processing and after separation ofthe thin sheet along perimeters 57. Because the surface modificationlayers control bonding energy to prevent permanent bonding of the thinsheet with the carrier, they may be used for processes whereintemperatures are ≧600° C. Of course, although these surface modificationlayers may control bonding surface energy during processing attemperatures≧600° C., they may also be used to produce a thin sheet andcarrier combination that will withstand processing at lowertemperatures, and may be used in such lower temperature applications.Moreover, where the thermal processing of the article will not exceed400° C., surface modification layers as exemplified by the examples 2c,2d, 4b may also be used—in some instances, depending upon the otherprocess requirements—in this same manner to control bonding surfaceenergy.

To Provide a Bonding Area

A third use of controlled bonding via surface modification layers(including materials and any associated bonding surface heat treatment)is to provide a bonding area between a glass carrier and a glass thinsheet. With reference to FIG. 6, a glass thin sheet 20 may be bonded toa glass carrier 10 by a bonded area 40.

In one embodiment of the third use, the bonded area 40, the carrier 10and thin sheet 20 may be covalently bonded to one another so that theyact as a monolith. Additionally, there are controlled bonding areas 50having perimeters 52, wherein the carrier 10 and thin sheet 20 arebonded to one another sufficient to withstand processing, and stillallow separation of the thin sheet from the carrier even after hightemperature processing, e.g. processing at temperatures≧600° C.Accordingly, surface modification layers 30 (including materials andbonding surface heat treatments) as exemplified by the examples 1a, 1b,1c, 2b, 2c, 2d, 4a, and 4b above, may be used to provide the bondingareas 40 between the carrier 10 and the thin sheet 20. Specifically,these surface modification layers and heat treatments may be formedoutside of the perimeters 52 of controlled bonding areas 50 either onthe carrier 10 or on the thin sheet 20. Accordingly, when the article 2is processed at high temperature, or is treated at high temperature toform covalent bonds, the carrier and the thin sheet 20 will bond to oneanother within the bonding area 40 outside of the areas bounded byperimeters 52. Then, during extraction of the desired parts 56 havingperimeters 57, when it is desired to dice the thin sheet 20 and carrier10, the article may be separated along lines 5 because these surfacemodification layers and heat treatments covalently bond the thin sheet20 with the carrier 10 so they act as a monolith in this area. Becausethe surface modification layers provide permanent covalent bonding ofthe thin sheet with the carrier, they may be used for processes whereintemperatures are ≧600° C. Moreover, where the thermal processing of thearticle, or of the initial formation of the bonding area 40, will be≧400° C. but less than 600° C., surface modification layers, asexemplified by the materials and heat treatments in example 4a may alsobe used in this same manner.

In a second embodiment of the third use, in the bonded area 40, thecarrier 10 and thin sheet 20 may be bonded to one another by controlledbonding via various surface modification layers described above.Additionally, there are controlled bonding areas 50, having perimeters52, wherein the carrier 10 and thin sheet 20 are bonded to one anothersufficient to withstand processing, and still allow separation of thethin sheet from the carrier even after high temperature processing, e.g.processing at temperatures≧600° C. Accordingly, if processing will beperformed at temperatures up to 600° C., and it is desired not to have apermanent or covalent bond in area 40, surface modification layers 30(including materials and bonding surface heat treatments) as exemplifiedby the examples 2e, 3a, 3b, 4c, 4d, and 4e above, may be used to providethe bonding areas 40 between the carrier 10 and the thin sheet 20.Specifically, these surface modification layers and heat treatments maybe formed outside of the perimeters 52 of controlled bonding areas 50,and may be formed either on the carrier 10 or on the thin sheet 20. Thecontrolled bonding areas 50 may be formed with the same, or with adifferent, surface modification layer as was formed in the bonding area40. Alternatively, if processing will be performed at temperatures onlyup to 400° C., and it is desired not to have a permanent or covalentbond in area 40, surface modification layers 30 (including materials andbonding surface heat treatments) as exemplified by the examples 2c, 2d,2e, 3a, 3b, 4b, 4c, 4d, 4e, above, may be used to provide the bondingareas 40 between the carrier 10 and the thin sheet 20.

Instead of controlled bonding in areas 50, there may be non-bondingregions in areas 50, wherein the non-bonding regions may be areas ofincreased surface roughness as described in US '727, or may be providedby surface modification layers as exemplified by example 2a.

For Bulk Annealing or Bulk Processing

A fourth use of the above-described manners of controlling bonding isfor bulk annealing of a stack of glass sheets. Annealing is a thermalprocess for achieving compaction of the glass. Compaction involvesreheating a glass body to a temperature below the glass softening point,but above the maximum temperature reached in a subsequent processingstep. This achieves structural rearrangement and dimensional relaxationin the glass prior to, rather than during, the subsequent processing.Annealing prior to subsequent processing is beneficial to maintainprecise alignment and/or flatness in a glass body during the subsequentprocessing, as in the manufacture of flat panel display devices, whereinstructures made of many layers need to be aligned with a very tighttolerance, even after being subject to high temperature environments. Ifthe glass compacts in one high temperature process, the layers of thestructures deposited onto the glass prior to the high temperatureprocess may not align correctly with the layers of the structuresdeposited after the high temperature process.

It is economically attractive to compact glass sheets in stacks.However, this necessitates interleaving, or separating, adjacent sheetsto avoid sticking. At the same time, it is beneficial to maintain thesheets extremely flat and with an optical-quality, or pristine, surfacefinish. Additionally, for certain stacks of glass sheets, for examplesheets having small surface area, it may be beneficial to have the glasssheets “stick” together during the annealing process so that they mayeasily be moved as a unit without separating, but readily separate fromone another (by peeling for example) after the annealing process so thatthe sheets may be individually used. Alternatively, it may be beneficialto anneal a stack of glass sheets wherein selected ones of the glasssheets are prevented from permanently bonding with one another, while atthe same time, allowing other ones of the glass sheets, or portions ofthose other glass sheets, e.g., their perimeters, to permanently bondwith each other. As still another alternative, it may be beneficial tostack glass sheets to, in bulk, selectively permanently bond theperimeters of selected adjacent pairs of the sheets in the stack. Theabove-described manners of controlling bonding between glass sheets maybe used to achieve the foregoing bulk annealing and/or selectivebonding. In order to control bonding at any particular interface betweenadjacent sheets, there may be used a surface modification layer on atleast one of the major surfaces facing that interface.

One embodiment of a stack of glass sheets, suitable for bulk annealingor bulk permanent bonding in selected areas (for example around theperimeter), will be described with reference to FIGS. 7 and 8. WhereinFIG. 7 is a schematic side view of a stack 760 of glass sheets 770-772,and FIG. 8 is an exploded view thereof for purposes of furtherexplanation.

A stack 760 of glass sheets may include glass sheets 770-772, andsurface modification layers 790 to control the bonding between the glasssheets 770-772. Additionally, the stack 760 may include cover sheets780, 781 disposed on the top and bottom of the stack, and may includesurface modification layers 790 between the covers and the adjacentglass sheets.

As shown in FIG. 8, each of the glass sheets 770-772 includes a firstmajor surface 776 and a second major surface 778. The glass sheets maybe made of any suitable glass material, for example, an alumino-silicateglass, a boro-silicate glass, or an alumino-boro-silicate glass.Additionally, the glass may be alkali containing, or may be alkali-free.Each of the glass sheets 770-772 may be of the same composition, or thesheets may be of different compositions. Further, the glass sheets maybe of any suitable type. That is, for example, the glass sheets 770-772may be all carriers as described above, may be all thin sheets asdescribed above, or may alternately be carriers and thin sheets. It isbeneficial to have a stack of carriers, and a separate stack of thinsheets when bulk annealing requires a different time-temperature cyclefor the carriers than for the thin sheets. Alternatively, with the rightsurface modification layer material and placement, it may be desirableto have a stack with alternate carriers and thin sheets, whereby ifdesired pairs of a carrier and a thin sheet, i.e., those forming anarticle, may be covalently bonded to one another in bulk for laterprocessing, while at the same time preserving the ability to separateadjacent articles from one another. Still further, there may be anysuitable number of glass sheets in the stack. That is, although onlythree glass sheets 770-772 are shown in FIGS. 7 and 8, any suitablenumber of glass sheets may be included in a stack 760.

In any particular stack 760 any one glass sheet may include no surfacemodification layers, one surface modification layer, or two surfacemodification layers. For example, as shown in FIG. 8, sheet 770 includesno surface modification layers, sheet 771 includes one surfacemodification layer 790 on its second major surface 778, and sheet 772includes two surface modification layers 790 wherein one such surfacemodification layer is on each of its major surfaces 776, 778.

The cover sheets 780, 781 may be any material that will suitablywithstand (not only in terms of time and temperature, but also withrespect to other pertinent considerations like outgassing, for example)the time-temperature cycle for a given process.

Advantageously, the cover sheets may be made of the same material as theglass sheets being processed. When the cover sheets 780, 781 arepresent, and are of a material that undesirably would bond with theglass sheets upon putting the stack through a given time-temperaturecycle, a surface modification layer 790 may be included between theglass sheet 771 and the cover sheet 781 and/or between the glass sheet772 and the cover sheet 780, as appropriate. When present between acover and a glass sheet, the surface modification layer may be on thecover (as shown with cover 781 and adjacent sheet 771), may be on theglass sheet (as shown with cover 780 and sheet 772), or may be on boththe cover and the adjacent sheet (not shown). Alternatively, if thecover sheets 780, 781 are present, but are of a material that will notbond with the adjacent sheets 772, 772, then surface modification layers790 need not be present therebetween.

Between adjacent sheets in the stack, there is an interface. Forexample, between adjacent ones of the glass sheets 770-772, there isdefined an interface, i.e., there is an interface 791 between sheet 770and sheet 771, and interface 792 between sheet 770 and sheet 772.Additionally, when the cover sheets 780, 781 are present, there is aninterface 793 between cover 781 and sheet 771, as well as an interface794 between sheet 772 and cover 780.

In order to control bonding at a given interface 791, 792 betweenadjacent glass sheets, or at a given interface 793, 794 between a glasssheet and a cover sheet, there may be used a surface modification layer790. For example, as shown, there is present at each interface 791, 792,a surface modification layer 790 on at least one of the major surfacesfacing that interface. For example, for interface 791, the second majorsurface 778 of glass sheet 771 includes a surface modification layer 790to control the bonding between sheet 771 and adjacent sheet 770.Although not shown, the first major surface 776 of sheet 770 could alsoinclude a surface modification layer 790 thereon to control bonding withsheet 771, i.e., there may be a surface modification layer on each ofthe major surfaces facing any particular interface.

The particular surface modification layer 790 (and any associatedsurface modification treatment—for example a heat treatment on aparticular surface prior to application of a particular surfacemodification layer to that surface, or a surface heat treatment of asurface with which a surface modification layer may contact) at anygiven interface 791-794, may be selected for the major surfaces 776, 778facing that particular interface 791-794 to control bonding betweenadjacent sheets and, thereby, achieve a desired outcome for a giventime-temperature cycle to which the stack 760 is subjected.

If it was desired to bulk anneal a stack of glass sheets 770-772 at atemperature up to 400° C., and to separate each of the glass sheets fromone another after the annealing process, then bonding at any particularinterface, for example interface 791, could be controlled using amaterial according to any one of the examples 2a, 2c, 2d, 2e, 3a, 3b, or4b-4e, together with any associated surface preparation. Morespecifically, the first surface 776 of sheet 770 would be treated as the“Thin Glass” in Tables 2-4, whereas the second surface 778 of sheet 771,would treated as the “Carrier” in Tables 2-4, or vice versa. A suitabletime-temperature cycle, having a temperature up to 400° C., could thenbe chosen based on the desired degree of compaction, number of sheets inthe stack, as well as size and thickness of the sheets, so as to achievethe requisite time-temperature throughout the stack.

Similarly, if it was desired to bulk anneal a stack of glass sheets770-772 at a temperature up to 600° C., and to separate each of theglass sheets from one another after the annealing process, then bondingat any particular interface, for example interface 791, could becontrolled using a material according to any one of the examples 2a, 2e,3a, 3b, 4c, 4d, 4e, together with any associated surface preparation.More specifically, the first surface 776 of sheet 770 would be treatedas the “Thin Glass” in Tables 2-4, whereas the second surface 778 ofsheet 771, would treated as the “Carrier” in Tables 2-4, or vice versa.A suitable time-temperature cycle, having a temperature up to 600° C.,could then be chosen based on the desired degree of compaction, numberof sheets in the stack, as well as size and thickness of the sheets, soas to achieve the requisite time-temperature throughout the stack.

Further, it is possible to preform bulk annealing, and bulk articleformation, by appropriately configuring the stack of sheets and thesurface modification layers between each pair of them. If it was desiredto bulk anneal a stack of glass sheets 770-772 at a temperature up to400° C., and then in-bulk covalently bond pairs of adjacent sheets toone another to form articles 2, suitable materials and associatedsurface preparation could be selected for controlling bonding. Forexample, around the peripheries (or at other desired bonding areas 40),the bonding at the interface between pairs of glass sheets to be formedinto an article 2, for example sheets 770 and 771, could be controlledusing: (i) a material according to any one of the examples 2c, 2d, 4b,together with any associated surface preparation, around the perimeter(or other desired bonding area 40) of the sheets 770, 771; and (ii) amaterial according to any one of the examples 2a, 2e, 3a, 3b, 4c, 4d,4e, together with any associated surface preparation, on an interiorarea (i.e., an area interior of the perimeter as treated in (i), or indesired controlled bonding areas 50 where separation of one sheet fromthe other is desired) of the sheets 770, 771. In this case, deviceprocessing in the controlled bonding areas 50 could then be performed attemperatures up to 600° C.

Materials and heat treatments could be appropriately selected forcompatibility with one another. For example, any of the materials 2c,2d, or 4b, could be used for the bonding areas 40 with a materialaccording to example 2a for the controlled bonding areas. Alternatively,the heat treatment for the bonding areas and controlled bonding areascould be appropriately controlled to minimize the effect of heattreatment in one area adversely affecting the desired degree of bondingin an adjacent area.

After appropriately selecting surface modification layers 790 andassociated heat treatments for the glass sheets in the stack, thosesheets could be appropriately arranged into a the stack and then heatedup to 400° C. to bulk anneal all the sheets in the stack without thembeing permanently bonded to one another. Then, the stack could be heatedup to 600° C. to form covalent bonds in the desired bonding areas of apair of adjacent sheets to form an article 2 having a pattern of bondingareas and controlled bonding areas. The bonding at the interface betweenone pair of sheets that are to be covalently bonded by bonding areas 40to form an article 2, and another pair of such sheets forming a separatebut adjacent article 2, could be controlled with the materials andassociated heat treatments of examples 2a, 2e, 3a, 3b, 4c, 4d, 4e, sothat adjacent articles 2 would not be covalently bonded to one another.In this same manner of controlling bonding between adjacent articles,there could be controlled the bonding between an article and any coversheet that is present in the stack.

Still further, similarly to the above, it is possible to form articles 2in bulk from a stack 760 without annealing that same stack 760beforehand. Instead, the sheets could have been separately annealed, orannealed in a different stack and separated therefrom, prior toconfiguring them for the desired controlled bonding in a stack toproduce articles in bulk. From the immediately above-described manner ofbulk annealing and then forming articles in bulk from one and the samestack, the bulk annealing is simply omitted.

Although only the manners of controlling bonding at interface 791 wereexplained in detail above, of course the same may be done at interface792, or for any other interface that may be present in a particularstack—as in the case of more than three glass sheets in a stack, or aswhen there is a cover sheet that would undesirably bond to a glasssheet. Further, although the same manner of controlling bonding may beused at any interfaces 791, 792, 793, 794 that are present, differentones of the above-described manners of controlling bonding may also beused at different interfaces to produce the same or a different outcomein terms of the type of bond desired.

In the above processes of bulk annealing, or forming articles 2 in bulk,when HMDS is used as a material for controlling bonding at an interface,and the HMDS is exposed to the outer periphery of the stack, the heatingabove about 400° C. should be performed in an oxygen-free atmospherewhen it is desired to prevent covalent bonding in the area of the HMDS.That is, if the HMDS is exposed to an amount of oxygen in the atmosphere(at a temperature above about 400° C.) sufficient to oxidize the HMDS,the bonding in any such area where the HMDS has been oxidized willbecome covalent bonding between adjacent glass sheets. Other alkylhydrocarbon silanes similarly can be affected by exposure to oxygen athigher temperatures, e.g., above about 400° C., e.g., ethyl, propyl,butyl, or steryl, silanes. Similarly, if using other materials for thesurface modification layer, the environment for the bulk annealingshould be chosen so that the materials will not degrade over thetime-temperature cycle of the anneal. As used herein, oxygen free maymean an oxygen concentration of less than 1000 ppm by volume, morepreferred less than 100 ppm by volume.

Once the stack of sheets has been bulk annealed, individual sheets maybe separated from the stack. The individual sheets can be treated (forexample, by oxygen plasma, heating in an oxygen environment at atemperature≧400° C., or by chemical oxidation, SC1, or SC2) to removethe surface modification layer 790. The individual sheets can be used asdesired, for example, as electronic device substrates, for example OLED,FPD, or PV devices).

The above-described methods of bulk annealing, or bulk processing, havethe advantage of maintaining clean sheet surfaces in an economicalmanner. More specifically, the sheets do not need to be kept in a cleanenvironment from start to finish, as in a clean-room annealing lehr.Instead, the stack can be formed in a clean environment, and thenprocessed in a standard annealing lehr (i.e., one in which cleanlinessis not controlled) without the sheet surfaces getting dirty withparticles because there is no fluid flow between the sheets.Accordingly, the sheet surfaces are protected from the environment inwhich the stack of sheets is annealed. After annealing, the stack ofsheets can be easily transported to a further processing area (either inthe same or a different facility) because the sheets maintain somedegree of adhesion, yet remain separable from one another uponsufficient force without damaging the sheets. That is, a glassmanufacturer (for example) can assemble and anneal a stack of glasssheets, and then ship the sheets as a stack wherein they remain togetherduring shipping (without fear of them separating in transit), whereuponarriving at their destination the sheets may be separated from the stackby a customer who may use the sheets individually or in smaller groups.Once separation is desired, the stack of sheets can again be processedin a clean environment (after washing the stack as necessary).

Example of Bulk Annealing

Glass substrates were used as-received from the fusion draw process. Thefusion drawn glass composition was (in mole %): SiO2 (67.7), Al2O3(11.0), B2O3 (9.8), CaO (8.7), MgO (2.3), SrO (0.5). Seven (7), 0.7 mmthick by 150 mm diameter, fusion drawn glass substrates were patternedby lithographic methods with 200 nm deep fiducials/verniers using HF.Two (2) nm of a plasma deposited fluoropolymer as a surface modificationlayer was coated on all bonding surfaces of all glass substrates, i.e.,each surface of a substrate that faced another substrate was coated,whereupon the resulting surface energy of each sheet surface wasapproximately 35 mJ/m². The 7 coated individual glass substrates wereplaced together to form a single, thick substrate (referred to as the“glass stack”). The glass stack was annealed in a nitrogen purged tubefurnace ramping from 30° C. to 590° C. over a 15 minute period, holding30 minutes at 590° C., then ramping down to about 230° C. over a 50minute period, then removing the glass stack from the furnace andcooling to room temperature of about 30° C. in about 10 minutes. Aftercooling, the substrates were removed from the furnace and easilyseparated into individual sheets (i.e., the samples did not permanentlybond, globally or locally) using a razor wedge. Compaction was measuredon each individual substrate by comparing the glass fiducials to anon-annealed quartz reference. The individual substrates were found tocompact about 185 ppm. Two of the substrates as individual samples (notstacked together) went through a second anneal cycle as described above(590° C./30 minute hold). Compaction was measured again and thesubstrates were found to further compact less than 10 ppm (actually 0 to2.5 ppm) due to the second heat treatment (change in glass dimensions—ascompared with original glass dimension—after the second heat treatmentminus the change in glass dimensions after the first heat treatment).Thusly, the inventors have demonstrated that individual glass sheets canbe coated, stacked, heat treated at a high temperature to achievecompaction, cooled, separated into individual sheets and have <10 ppm,and even <5 ppm in dimension change (as compared to their size after thefirst heat treatment) after a second heat treatment.

Although the furnace in the above-described annealing example was purgedwith nitrogen, annealing furnaces may also be purged with other gassesincluding, air, argon, oxygen, CO₂, or combinations thereof, dependingupon the annealing temperature, and the stability of the surfacemodification layer material at those temperatures in a particularenvironment.

Additionally, although not shown, the glass may be annealed in a spool,instead of sheet, form. That is, a suitable surface modification layermay be formed on one or both sides of a glass ribbon, and the ribbonthen rolled. The entire roll could be subject to the same treatment asnoted above for sheets, whereupon the glass of the entire spool would beannealed without sticking one wrap of the glass to an adjacent one. Uponun-rolling, the surface modification layer may be removed by anysuitable process.

Outgassing

Polymer adhesives used in typical wafer bonding applications aregenerally 10-100 microns thick and lose about 5% of their mass at ornear their temperature limit. For such materials, evolved from thickpolymer films, it is easy to quantify the amount of mass loss, oroutgassing, by mass-spectrometry. On the other hand, it is morechallenging to measure the outgassing from thin surface treatments thatare on the order of 10 nm thick or less, for example the plasma polymeror self-assembled monolayer surface modification layers described above,as well as for a thin layer of pyrolyzed silicone oil. For suchmaterials, mass-spectrometry is not sensitive enough. There are a numberof other ways to measure outgassing, however.

A first manner of measuring small amounts of outgassing is based onsurface energy measurements, and will be described with reference toFIG. 9. To carry out this test, a setup as shown in FIG. 9 may be used.A first substrate, or carrier, 900 having the to-be-tested surfacemodification layer thereon presents a surface 902, i.e., a surfacemodification layer corresponding in composition and thickness to thesurface modification layer 30 to be tested. A second substrate, orcover, 910 is placed so that its surface 912 is in close proximity tothe surface 902 of the carrier 900, but not in contact therewith. Thesurface 912 is an uncoated surface, i.e., a surface of bare materialfrom which the cover is made. Spacers 920 are placed at various pointsbetween the carrier 900 and cover 910 to hold them in spaced relationfrom one another. The spacers 920 should be thick enough to separate thecover 910 from the carrier 900 to allow a movement of material from oneto the other, but thin enough so that during testing the amount ofcontamination from the chamber atmosphere on the surfaces 902 and 912 isminimized. The carrier 900, spacers 920, and cover 910, together form atest article 901.

Prior to assembly of the test article 901, the surface energy of baresurface 912 is measured, as is the surface energy of the surface 902,i.e., the surface of carrier 900 having the surface modification layerprovided thereon. The surface energies as shown in FIG. 10, both polarand dispersion components, were measured by fitting a theoretical modeldeveloped by S. Wu (1971) to three contact angles of three test liquids;water, diiodomethane and hexadecane. (Reference: S. Wu, J. Polym. Sci.C, 34, 19, 1971).

After assembly, the test article 901 is placed into a heating chamber930, and is heated through a time-temperature cycle. The heating isperformed at atmospheric pressure and under flowing N2 gas, i.e.,flowing in the direction of arrows 940 at a rate of 2 standard litersper minute.

During the heating cycle, changes in the surface 902 (including changesto the surface modification layer due to evaporation, pyrolysis,decomposition, polymerization, reaction with the carrier, andde-wetting, for example) are evidenced by a change in the surface energyof surface 902. A change in the surface energy of surface 902 by itselfdoes not necessarily mean that the surface modification layer hasoutgassed, but does indicate a general instability of the material atthat temperature as its character is changing due to the mechanismsnoted above, for example. Thus, the less the change in surface energy ofsurface 902, the more stable the surface modification layer. On theother hand, because of the close proximity of the surface 912 to thesurface 902, any material outgassed from surface 902 will be collectedon surface 912 and will change the surface energy of surface 912.Accordingly, the change in surface energy of surface 912 is a proxy foroutgassing of the surface modification layer present on surface 902.

Thus, one test for outgassing uses the change in surface energy of thecover surface 912. Specifically, if there is a change in surfaceenergy—of surface 912—of ≧10 mJ/m2, then there is outgassing. Changes insurface energy of this magnitude are consistent with contamination whichcan lead to loss of film adhesion or degradation in material propertiesand device performance. A change in surface energy of ≦5 mJ/m2 is closeto the repeatability of surface energy measurements and inhomogeneity ofthe surface energy. This small change is consistent with minimaloutgassing.

During testing that produced the results in FIG. 10, the carrier 900,the cover 910, and the spacers 920, were made of Eagle XG glass, analkali-free alumino-boro-silicate display-grade glass available fromCorning Incorporated, Corning, N.Y., although such need not be the case.The carrier 900 and cover 910 were 150 mm diameter 0.63 mm thick.Generally, the carrier 910 and cover 920 will be made of the samematerial as carrier 10 and thin sheet 20, respectively, for which anoutgassing test is desired. During this testing, silicon spacers 0.63 mmthick, 2 mm wide, and 8 cm long, thereby forming a gap of 0.63 mmbetween surfaces 902 and 912. During this testing, the chamber 930 wasincorporated in MPT-RTP600s rapid thermal processing equipment that wascycled from room temperature to the test limit temperature at a rate of9.2° C. per minute, held at the test limit temperature for varying timesas shown in the graphs as “Anneal Time”, and then cooled at furnace rateto 200° C. After the oven had cooled to 200° C., the test article wasremoved, and after the test article had cooled to room temperature, thesurface energies of each surface 902 and 912 were again measured. Thus,by way of example, using the data for the change in cover surfaceenergy, tested to a limit temperature of 450° C., for Material #1, line1003, the data was collected as follows. The data point at 0 minutesshows a surface energy of 75 mJ/m2 (milli-Joules per square meter), andis the surface energy of the bare glass, i.e., there has been notime-temperature cycle yet run. The data point at one minute indicatesthe surface energy as measured after a time-temperature cycle performedas follows: the article 901 (having Material #1 used as a surfacemodification layer on the carrier 900 to present surface 902) was placedin a heating chamber 930 at room temperature, and atmospheric pressure;the chamber was heated to the test-limit temperature of 450° C. at arate of 9.2° C. per minute, with a N2 gas flow at two standard litersper minute, and held at the test-limit temperature of 450° C. for 1minute; the chamber was then allowed to cool to 300° C. at a rate of 1°C. per minute, and the article 901 was then removed from the chamber930; the article was then allowed to cool to room temperature (withoutN2 flowing atmosphere); the surface energy of surface 912 was thenmeasured and plotted as the point for 1 minute on line 1003. Theremaining data points for Material #1 (lines 1003, 1004), as well as thedata points for Material #2 (lines 1203, 1204), Material #3 (lines 1303,1304), Material #4 (lines 1403, 1404), Material #5 (lines 1503, 1504),and Material #6 (lines 1603, and 1604), were then determined in asimilar manner with the minutes of anneal time corresponding to the holdtime at the test-limit temperature, either 450° C., or 600° C., asappropriate. The data points for lines 1001, 1002, 1201, 1202, 1301,1302, 1401, 1402, 1501, 1502, 1601, and 1602, representing surfaceenergy of surface 902 for the corresponding surface modification layermaterials (Materials #1-6) were determined in a similar manner, exceptthat the surface energy of the surface 902 was measured after eachtime-temperature cycle.

The above assembly process, and time-temperature cycling, were carriedout for six different materials as set forth below, and the results aregraphed in FIG. 10. Of the six materials, Materials #1-4 correspond tosurface modification layer materials described above. Materials #5 and#6 are comparative examples.

Material #1 is a CHF3-CF4 plasma polymerized fluoropolymer. Thismaterial is consistent with the surface modification layer in example3b, above. As shown in FIG. 10, lines 1001 and 1002 show that thesurface energy of the carrier did not significantly change. Thus, thismaterial is very stable at temperatures from 450° C. to 600° C.Additionally, as shown by the lines 1003 and 1004, the surface energy ofthe cover did not significantly change either, i.e., the change is ≦5mJ/m2. Accordingly, there was no outgassing associated with thismaterial from 450° C. to 600° C.

Material #2 is a phenylsilane, a self-assembled monolayer (SAM)deposited form 1% toluene solution of phenyltriethoxysilane and cured invacuum oven 30 minutes at 190° C. This material is consistent with thesurface modification layer in example 4c, above. As shown in FIG. 10,lines 1201 and 1202 indicate some change in surface energy on thecarrier. As noted above, this indicates some change in the surfacemodification layer, and comparatively, Material #2 is somewhat lessstable than Material #1. However, as noted by lines 1203 and 1204, thechange in surface energy of the carrier is ≦5 mJ/m2, showing that thechanges to the surface modification layer did not result in outgassing.

Material #3 is a pentafluorophenylsilane, a SAM deposited from 1%toluene solution of pentafluorophenyltriethoxysilane and cured in vacuumoven 30 minutes at 190° C. This material is consistent with the surfacemodification layer in example 4e, above. As shown in FIG. 10, lines 1301and 1302 indicate some change in surface energy on the carrier. As notedabove, this indicates some change in the surface modification layer, andcomparatively, Material #3 is somewhat less stable than Material #1.However, as noted by lines 1303 and 1304, the change in surface energyof the carrier is ≦5 mJ/m2, showing that the changes to the surfacemodification layer did not result in outgassing.

Material #4 is hexamethyldisilazane (HMDS) deposited from vapor in a YESHMDS oven at 140° C. This material is consistent with the surfacemodification layer in Example 2b, of Table 2, above. As shown in FIG.10, lines 1401 and 1402 indicate some change in surface energy on thecarrier. As noted above, this indicates some change in the surfacemodification layer, and comparatively, Material #4 is somewhat lessstable than Material #1. Additionally, the change in surface energy ofthe carrier for Material #4 is greater than that for any of Materials #2and #3 indicating, comparatively, that Material #4 is somewhat lessstable than Materials #2 and #3. However, as noted by lines 1403 and1404, the change in surface energy of the carrier is ≦5 mJ/m2, showingthat the changes to the surface modification layer did not result inoutgassing that affected the surface energy of the cover. However, thisis consistent with the manner in which HMDS outgasses. That is, HMDSoutgasses ammonia and water which do not affect the surface energy ofthe cover, and which may not affect some electronics fabricationequipment and/or processing. On the other hand, when the products of theoutgassing are trapped between the thin sheet and carrier, there may beother problems, as noted below in connection with the second outgassingtest.

Material #5 is Glycidoxypropylsilane, a SAM deposited from 1% toluenesolution of glycidoxypropyltriethoxysilane and cured in vacuum oven 30minutes at 190° C. This is a comparative example material. Althoughthere is relatively little change in the surface energy of the carrier,as shown by lines 1501 and 1502, there is significant change in surfaceenergy of the cover as shown by lines 1503 and 1504. See FIG. 10. Thatis, although Material #5 was relatively stable on the carrier surface,it did, indeed outgas a significant amount of material onto the coversurface whereby the cover surface energy changed by ≧10 mJ/m2. Althoughthe surface energy at the end of 10 minutes at 600° C. is within 10mJ/m2, the change during that time does exceed 10 mJ/m2. See, forexample the data points at 1 and 5 minutes. Although not wishing to bebound by theory, the slight uptick in surface energy from 5 minutes to10 minutes is likely do to some of the outgassed material decomposingand falling off of the cover surface.

Material #6 is DC704 a silicone coating prepared by dispensing 5 ml DowCorning 704 diffusion pump oil tetramethyltetraphenyl trisiloxane(available from Dow Corning) onto the carrier, placing it on a 500° C.hot plate in air for 8 minutes. Completion of sample preparation isnoted by the end of visible smoking. After preparing the sample in theabove manner, the outgassing testing described above was carried out.This is a comparative example material. As shown in FIG. 10, lines 1601and 1602 indicate some change in surface energy on the carrier. As notedabove, this indicates some change in the surface modification layer, andcomparatively, Material #6 is less stable than Material #1.Additionally, as noted by lines 1603 and 1604, the change in surfaceenergy of the carrier is ≧10 mJ/m2, showing significant outgassing. Moreparticularly, at the test-limit temperature of 450° C., the data pointfor 10 minutes shows a decrease in surface energy of about 15 mJ/m2, andeven greater decrease in surface energy for the points at 1 and 5minutes. Similarly, the change in surface energy of the cover duringcycling at the 600° C. test-limit temperature, the decrease in surfaceenergy of the cover was about 25 mJ/m2 at the 10 minute data point,somewhat more at 5 minutes, and somewhat less at 1 minute. Altogether,though, a significant amount of outgassing was shown for this materialover the entire range of testing.

Significantly, for Materials #1-4, the surface energies throughout thetime-temperature cycling indicate that the cover surface remains at asurface energy consistent with that of bare glass, i.e., there iscollected no material outgassed from the carrier surface. In the case ofMaterial #4, as noted in connection with Table 2, the manner in whichthe carrier and thin sheet surfaces are prepared makes a big differencein whether an article (thin sheet bonded together with a carrier via asurface modification layer) will survive FPD processing. Thus, althoughthe example of Material #4 shown in FIG. 10 may not outgas, thismaterial may or may not survive the 400° C. or 600° C. tests as noted inconnection with the discussion of Table 2.

A second manner of measuring small amounts of outgassing is based on anassembled article, i.e., one in which a thin sheet is bonded to acarrier via a surface modification layer, and uses a change in percentbubble area to determine outgassing. That is, during heating of thearticle, bubbles formed between the carrier and the thin sheet indicateoutgassing of the surface modification layer. As noted above inconnection with the first outgassing test, it is difficult to measureoutgassing of very thin surface modification layers. In this secondtest, the outgassing under the thin sheet may be limited by strongadhesion between the thin sheet and carrier. Nonetheless, layers≦10 nmthick (plasma polymerized materials, SAMs, and pyrolyzed silicone oilsurface treatments, for example) may still create bubbles during thermaltreatment, despite their smaller absolute mass loss. And the creation ofbubbles between the thin sheet and carrier may cause problems withpattern generation, photolithography processing, and/or alignment duringdevice processing onto the thin sheet. Additionally, bubbling at theboundary of the bonded area between the thin sheet and the carrier maycause problems with process fluids from one process contaminating adownstream process. A change in % bubble area of ≧5 is significant,indicative of outgassing, and is not desirable. On the other hand achange in % bubble area of ≦1 is insignificant and an indication thatthere has been no outgassing.

The average bubble area of bonded thin glass in a class 1000 clean roomwith manual bonding is 1%. The % bubbles in bonded carriers is afunction of cleanliness of the carrier, thin glass sheet, and surfacepreparation. Because these initial defects act as nucleation sites forbubble growth after heat treatment, any change in bubble area upon heattreatment less than 1% is within the variability of sample preparation.To carry out this test, a commercially available desktop scanner withtransparency unit (Epson Expression 10000XL Photo) was used to make afirst scan image of the area bonding the thin sheet and carrierimmediately after bonding. The parts were scanned using the standardEpson software using 508 dpi (50 micron/pixel) and 24 bit RGB. The imageprocessing software first prepares an image by stitching, as necessary,images of different sections of a sample into a single image andremoving scanner artifacts (by using a calibration reference scanperformed without a sample in the scanner). The bonded area is thenanalyzed using standard image processing techniques such asthresholding, hole filling, erosion/dilation, and blob analysis. Thenewer Epson Expression 11000XL Photo may also be used in a similarmanner. In transmission mode, bubbles in the bonding area are visible inthe scanned image and a value for bubble area can be determined. Then,the bubble area is compared to the total bonding area (i.e., the totaloverlap area between the thin sheet and the carrier) to calculate a %area of the bubbles in the bonding area relative to the total bondingarea. The samples are then heat treated in a MPT-RTP600s Rapid ThermalProcessing system under N2 atmosphere at test-limit temperatures of 300°C., 450° C., and 600° C., for up to 10 minutes. Specifically, thetime-temperature cycle carried out included: inserting the article intothe heating chamber at room temperature and atmospheric pressure; thechamber was then heated to the test-limit temperature at a rate of 9° C.per minute; the chamber was held at the test-limit temperature for 10minutes; the chamber was then cooled at furnace rate to 200° C.; thearticle was removed from the chamber and allowed to cool to roomtemperature; the article was then scanned a second time with the opticalscanner. The % bubble area from the second scan was then calculated asabove and compared with the % bubble area from the first scan todetermine a change in % bubble area (A % bubble area). As noted above, achange in bubble area of ≧5% is significant and an indication ofoutgassing. A change in % bubble area was selected as the measurementcriterion because of the variability in original % bubble area. That is,most surface modification layers have a bubble area of about 2% in thefirst scan due to handling and cleanliness after the thin sheet andcarrier have been prepared and before they are bonded. However,variations may occur between materials. The same Materials #1-6 setforth with respect to the first outgassing test method were again usedin this second outgassing test method. Of these materials, Materials#1-4 exhibited about 2% bubble area in the first scan, whereas Materials#5 and #6 showed significantly larger bubble area, i.e., about 4%, inthe first scan.

The results of the second outgassing test will be described withreference to FIGS. 11 and 12. The outgassing test results for Materials#1-3 are shown in FIG. 11, whereas the outgassing test results forMaterials #4-6 are shown in FIG. 12.

The results for Material #1 are shown as square data points in FIG. 11.As can be seen from the figure, the change in % bubble area was nearzero for test-limit temperatures of 300° C., 450° C., and 600° C.Accordingly, Material #1 shows no outgassing at these temperatures.

The results for Material #2 are shown as diamond data points in FIG. 11.As can be seen from the figure, the change in % bubble area is less than1 for test-limit temperatures of 450° C. and 600° C. Accordingly,Material #2 shows no outgassing at these temperatures.

The results for Material #3 are shown as triangle data points in FIG.11. As can be seen from the figure, similar to the results for Material#1, the change in % bubble area was near zero for test-limittemperatures of 300° C., 450° C., and 600° C. Accordingly, Material #1shows no outgassing at these temperatures.

The results for Material #4 are shown as circle data points in FIG. 12.As can be seen from the figure, the change in % bubble area is near zerofor the test-limit temperature of 300° C., but is near 1% for somesamples at the test-limit temperatures of 450° C. and 600° C., and forother samples of that same material is about 5% at the test limittemperatures of 450° C. and 600° C. The results for Material #4 are veryinconsistent, and are dependent upon the manner in which the thin sheetand carrier surfaces are prepared for bonding with the HMDS material.The manner in which the samples perform being dependent upon the mannerin which the samples are prepared is consistent with the examples, andassociated discussion, of this material set forth in connection withTable 2 above. It was noted that, for this material, the samples havinga change in % bubble area near 1%, for the 450° C. and 600° C.test-limit temperatures, did not allow separation of the thin sheet fromthe carrier according to the separation tests set forth above. That is,a strong adhesion between the thin sheet and carrier may have limitedbubble generation. On the other hand, the samples having a change in %bubble area near 5% did allow separation of the thin sheet from thecarrier. Thus, the samples that had no outgassing had the undesiredresult of increased adhesion after temperature treatment which stickingthe carrier and thin sheet together (preventing removal of the thinsheet from the carrier), whereas the samples that allowed removal of thethin sheet and carrier had the undesired result of outgassing.

The results for Material #5 are shown in FIG. 12 as triangular datapoints. As can be seen from the figure, the change in % bubble area isabout 15% for the test-limit temperature of 300° C., and is well overthat for the higher test-limit temperatures of 450° C. and 600° C.Accordingly, Material #5 shows significant outgassing at thesetemperatures.

The results for Material #6 are shown as square data points in FIG. 12.As can be seen from this figure, the change in % bubble area is over2.5% for the test-limit temperature of 300° C., and is over 5% for thetest limit-temperatures of 450° C. and 600° C. Accordingly, Material #6shows significant outgassing at the test-limit temperatures of 450° C.and 600° C.

CONCLUSION

It should be emphasized that the above-described embodiments of thepresent invention, particularly any “preferred” embodiments, are merelypossible examples of implementations, merely set forth for a clearunderstanding of various principles of the invention. Many variationsand modifications may be made to the above-described embodiments of theinvention without departing substantially from the spirit and variousprinciples of the invention. All such modifications and variations areintended to be included herein within the scope of this disclosure andthe present invention and protected by the following claims.

For example, although the surface modification layer 30 of manyembodiments is shown and discussed as being formed on the carrier 10, itmay instead, or in addition, be formed on the thin sheet 20. That is,the materials as set forth in the examples 4 and 3 may be applied to thecarrier 10, to the thin sheet 20, or to both the carrier 10 and thinsheet 20 on faces that will be bonded together.

Further, although some surface modification layers 30 were described ascontrolling bonding strength so as to allow the thin sheet 20 to beremoved from the carrier 10 even after processing the article 2 attemperatures of 400° C., or of 600° C., of course it is possible toprocess the article 2 at lower temperatures than those of the specifictest the article passed and still achieve the same ability to remove thethin sheet 20 from the carrier 10 without damaging either the thin sheet20 or the carrier 10.

Still further, although the controlled bonding concepts have beendescribed herein as being used with a carrier and a thin sheet, incertain circumstances they are applicable to controlling bonding betweenthicker sheets of glass, ceramic, or glass ceramic, wherein it may bedesired to detach the sheets (or portions of them) from each other.

Further yet, although the controlled bonding concepts herein have beendescribed as being useful with glass carriers and glass thin sheets, thecarrier may be made of other materials, for example, ceramic, glassceramic, or metal. Similarly, the sheet controllably bonded to thecarrier may be made of other materials, for example, ceramic or glassceramic.

According to a first aspect, there is provided a method of annealingglass sheets, comprising:

stacking a plurality of glass sheets, each of the glass sheets havingtwo major surfaces, so that interfaces are defined between adjacent onesof the glass sheets in the plurality of glass sheets, wherein there isdisposed on at least one of the major surfaces that faces one of theinterfaces, a surface modification layer;

exposing the stack of glass sheets to a time-temperature cyclesufficient to compact each of the glass sheets,

wherein the surface modification layer is sufficient to control,throughout the time-temperature cycle, bonding between the adjacent onesof the glass sheets in the stack defining the one of the interfaces,wherein bonding is controlled to be of such a force so that one sheetdoes not separate from another if one is held and the other subjected tothe force of gravity, but so that the sheets may be separated withoutbreaking one of the adjacent ones of the glass sheets into two or morepieces.

According to a second aspect, there is provided the method of aspect 1,wherein the time-temperature cycle includes a temperature≧400° C., butless than the strain point of the glass sheets.

According to a third aspect, there is provided the method of aspect 1,wherein the time-temperature cycle includes a temperature≧600° C., butless than the strain point of the glass sheets.

According to a fourth aspect, there is provided the method of any one ofaspects 1 to 3, wherein the surface modification layer is one of HMDS, aplasma polymerized fluoropolymer, and an aromatic silane.

According to a fifth aspect, there is provided the method of aspect 4,wherein when the surface modification layer comprises a plasmapolymerized fluoropolymer, the surface modification layer is one of:plasma polymerized polytetrafluroethylene; and a plasma polymerizedfluoropolymer surface modification layer deposited from a CF4-C4F8mixture having ≦40% C4F8.

According to a sixth aspect, there is provided the method of aspect 4,wherein when the surface modification layer comprises an aromaticsilane, the surface modification layer is a phenyl silane.

According to a seventh aspect, there is provided the method of aspect 4,wherein when the surface modification layer comprises an aromaticsilane, the surface modification layer is one of: phenyltriethoxysilane;diphenyldiethoxysilane; and 4-pentafluorophenyltriethoxysilane.

According to an eighth aspect, there is provided the method of any oneof aspects 4-7, wherein the time-temperature cycle is carried out in anoxygen-free environment.

1-8. (canceled)
 9. A method of annealing glass, comprising: stacking aplurality of glass layers, each of the glass layers having two majorsurfaces, so that interfaces are defined between adjacent ones of theglass layers in the plurality of glass layers, wherein the stack ofglass layers comprises a rolled sheet of glass, and wherein there isdisposed on at least one of the major surfaces that faces one of theinterfaces, a surface modification layer; exposing the stack of glasslayers to a time-temperature cycle sufficient to compact each of theglass layers, wherein the surface modification layer is sufficient tocontrol, throughout the time-temperature cycle, bonding between theadjacent ones of the glass layers in the stack defining the one of theinterfaces, wherein bonding is controlled to be of such a force so thatone layer does not separate from another if one is held and the othersubjected to the force of gravity, but so that the layers may beseparated without breaking one of the adjacent ones of the glass layersinto two or more pieces.
 10. The method of claim 9, wherein thetime-temperature cycle includes a temperature≧400° C., but less than thestrain point of the glass.
 11. The method of claim 9, wherein thetime-temperature cycle includes a temperature≧600° C., but less than thestrain point of the glass.
 12. The method of claim 9, wherein thesurface modification layer is one of HMDS, a plasma polymerizedfluoropolymer, and an aromatic silane.
 13. The method of claim 12,wherein when the surface modification layer comprises a plasmapolymerized fluoropolymer, the surface modification layer is one of:plasma polymerized polytetrafluroethylene; and a plasma polymerizedfluoropolymer surface modification layer deposited from a CF4-C4F8mixture having ≦40% C4F8.
 14. The method of claim 12, wherein when thesurface modification layer comprises an aromatic silane, the surfacemodification layer is a phenyl silane.
 15. The method of claim 12,wherein when the surface modification layer comprises an aromaticsilane, the surface modification layer is one of: phenyltriethoxysilane;diphenyldiethoxysilane; and 4-pentafluorophenyltriethoxysilane.
 16. Themethod of claim 9, wherein the time-temperature cycle is carried out inan oxygen-free environment.
 17. The method of claim 9, wherein the atleast one of the major surfaces having the surface modification layerthereon has a surface energy of ≧40 mJ/m².
 18. The method of claim 9,adhesion energy between the major surfaces of the layers facing the oneof the interfaces is greater than about 24 mJ/m².
 19. The method ofclaim 9, adhesion energy between the major surfaces of the layers facingthe one of the interfaces is from 50 to 1000 mJ/m2.